Browse Articles

Two-and-a-half decades of progress in mid-infrared AlGaN/GaN inter-subband light emitters

In this paper, the physics of AlGaN/GaN inter-subband (ISB) light emitters is presented. The important milestones of this research, including the relatively slow and winding early stages of device design, fabrication and characterization, will be highlighted. Special attention will be paid to the years around the turn of the millennium, during which we had already obtained most of the presented results. After several unsuccessful attempts to “push” these measurement results through a scientific journal review in 1999 already, they could be successfully published in “Applied Physics Letters” in 2014. In retrospect, five problematic areas are identified: First, a complete ignorance of the piezo- and pyro-electric polarization fields, although they were known since 1997 already. Second, a too low n-type doping, having resulted in an inefficient current transport and overly noisy signals at the interesting wavelength. Third, a coincidental match between GaN-based ISB transition and LO-phonon showing a narrow emission peak, which was consistently described many years later only. Fourth, the above-mentioned emission, which had revealed a pronounced spectral asymmetry. And fifth, the discovery of several experimental facts, which potentially allow a more careful analysis of this asymmetric emission. These five initially neglected issues, which were between 2014 and 2026, successively understood, will in this paper be concisely presented and carefully analyzed.

Intriguing optoelectronic properties of 2D Ca2ZrSe4 chalcogenide perovskite from first principles

Chalcogenide perovskites (CPs) have been attracting great attention as a promising light absorber for the next-generation perovskite solar cells (PSCs), but a deep insight into their material properties is not yet provided. In this work, we report a first-principles study of optoelectronic properties of two-dimensional (2D) CP Ca2ZrSe4 using the GW method combined with the Bethe–Salpeter equation and the Boltzmann transport equation methods. Our calculations demonstrate that one-layer (1L) Ca2ZrSe4 has a direct bandgap of 1.96 eV, light carrier effective masses, and large light absorption coefficients over 105 cm−1 for the visible light region. Furthermore, we find a relatively high electron/hole mobility of 432/64 cm2 V−1 s−1 and a high spectroscopically limited maximum efficiency of 34.4% at room temperature, highlighting the potential of 1L Ca2ZrSe4 as a promising light absorber for PSCs.

Enhancement of multiferroic response in La-doped PbTiO3–TbFeO3 perovskite

A novel solid solution of La-doped 0.80PbTiO3-0.20Tb(1−x)LaxFeO3, in the range 0.02 ≤ x ≤ 0.15, was studied for ferroelectric, electromechanical, and magnetic properties. Notably, at x = 0.08, the material exhibits enhanced characteristics, including a maximum remanent polarization of 37 μC/cm2. Structural analysis indicates that x = 0.08 corresponds to a phase boundary region separating the coexistence of tetragonal (P4mm) + cubic (Pm-3m) phases and a single tetragonal phase (P4mm), highlighting the critical role of phase boundary region in enhancing properties.

Enhanced Curie temperature and large spin Hall conductivity due to the magnetic proximity effect in CrI3/Pt heterostructures

Metal/van der Waals (vdW) heterostructures enable versatile interfacial spin control for spintronic applications. Using density-functional theory, we investigate the interfacial magnetic proximity effect and spin-transport response in CrI3/Pt bilayer heterostructures. The proximity effect not only raises the Curie temperature of CrI3 from 45 to 70 K but also induces interfacial spin polarization in the Pt surface layers. This behavior is consistent with orbital-selective hybridization involving Pt dxz/yz and dz2 states, which generates pronounced spin polarization near the Fermi level. Within the same computational setup, the Pt layer in the CrI3/Pt heterostructure exhibits a spin Hall conductivity (σSH) of 2890 S cm−1, corresponding to an enhancement of about 45% relative to an isolated Pt slab with the same thickness and in-plane lattice constant. This high efficiency persists in CrI3/Pt/Co trilayers, suggesting potential device relevance. Our results suggest that interfacial orbital reconstruction plays an important role in interfacial magnetism and spin transport in vdW magnets, and that CrI3/Pt provides a viable platform for efficient spin–orbit torque generation in two-dimensional spintronic devices.

<i>In situ</i> estimation of local acoustic pressure amplitude by force balancing with a ferrofluid droplet probe

Acoustic tweezers enable non-contact manipulation of microscale objects, but quantitative in situ evaluation of the peak local pressure amplitude remains difficult in confined devices. Conventional hydrophone-based measurements are often limited at the microscale by probe size and installation constraints. Here, we present a force-balance method in which a trapped ferrofluid droplet serves as a local probe in a standing-wave acoustic field, and an externally applied magnetic field gradient is tuned so that the magnetic force balances the maximum primary acoustic radiation force on the droplet. From the magnetic force on the ferrofluid droplet, determined at the balance point, we estimate a peak local pressure amplitude of 2.2×105 Pa for 7.2 MHz operation at 10 Vpp. This approach provides a practical route for quantitative in situ characterization of microscale acoustic fields and for setting operating conditions in compact acoustofluidic devices.

Wide-field magnetic imaging of shielding-current-driven vortex rearrangement under local heating using diamond quantum sensors

Understanding and controlling vortex motion in superconductors are important both for suppressing dissipation in superconducting devices and for device applications that exploit vortices. In this work, we quantitatively imaged the stray magnetic field distribution of vortices in an NbN thin film by wide-field magnetic imaging using a perfectly aligned diamond nitrogen-vacancy ensemble. By continuously measuring while stepwise varying the applied magnetic field under local laser heating, we captured a rearrangement of the vortex configuration in real space and in real time over more than 100 min. The observed vortex rearrangement is consistent with a reduction of the pinning force due to local laser heating and with the Lorentz force exerted by shielding currents induced by the field variation. These results provide insight into vortex dynamics and suggest potential applications, including vortex exclusion from sensitive regions of superconducting devices.

Enhanced energy storage performance in PbZrO3 antiferroelectric films through synergistic doping and strain strategies

Antiferroelectric thin films, particularly PbZrO3-based systems, are attractive for advanced energy storage due to their field-induced phase transitions and high dielectric responses. However, achieving high energy storage density remains challenging in such film system, because the competition between ferroelectric and antiferroelectric phases in antiferroelectric thin films is very sensitive. In this study, we tackle the common challenges of insufficient polarization in PbZrO3 epitaxial films by introducing Y at the A-site and employing compressive strain simultaneously. Consequently, the Y-doped PbZrO3 epitaxial film exhibits a significantly enhanced maximum polarization (Pm) of 128.89 μC/cm2 and an impressive energy storage density (Ue) of 44.73 J/cm3. This work demonstrates the effectiveness of synergistic doping and strain strategies for designing high-performance antiferroelectric energy storage materials.

Dual-path gain in Si-based ZnGa2O4 MOSFET solar-blind ultraviolet phototransistors

Solar-blind ultraviolet (UV) photodetection on silicon platforms is an important step toward practical optoelectronic integration. Here, we demonstrate a bottom-gate ZnGa2O4 metal-oxide-semiconductor field-effect transistor (MOSFET) solar-blind UV photodetector on a Si substrate with a Si3N4 gate dielectric. The device exhibits n-channel enhancement-mode operation with an on/off current ratio of ∼108 and a picoampere-level off-state current. Under solar-blind UV illumination, the phototransistor achieves a peak responsivity of 1.09 × 103 A/W, a detectivity of 1.74 × 1013 Jones, a UV-to-visible rejection ratio of 2.6 × 105, and rise/decay times of 22.7/19.2 ms. The photo-induced shift in the capacitance–voltage characteristics suggests the participation of charge trapping at the Si3N4/ZnGa2O4 interface, while cathodoluminescence and electrical analyses identify compensating zinc vacancy (VZn) acceptor defects coexisting with Ga-on-Zn (GaZn) antisite donors within the ZnGa2O4 channel. These trap states sustain two parallel gain pathways within the MOSFET architecture: vertical threshold-voltage modulation amplified through the subthreshold characteristic, and lateral photoconductive gain arising from carrier lifetime extension via hole capture by VZn acceptor defects. By distributing the total gain across two amplification channels rather than relying on prolonged carrier lifetime alone, this architecture offers a route to balanced high-gain and fast-response solar-blind UV detection on Si platforms compatible with CMOS technology.

Cluster-assembled CdO polymorph: A semiconductor with high carrier mobility and superior optical performance

Using the magic cluster Cd8O8 and a C linker, we constructed a new CdO polymorph, Tet-CdO, via bottom-up assembly. Tet-CdO exhibits good mechanical, thermal, and dynamical stability, with a B1-to-Tet transition at ∼322 K or −5.3 GPa, offering a viable synthetic route. With an optimal direct bandgap of 1.58 eV (HSE06), high absorption, low reflection, and high carrier mobility (up to 13.2 × 103 cm2 V−1 s−1), Tet-CdO achieves a theoretical photoconversion efficiency of 30.8%. A pronounced electron–hole mobility imbalance causes space charge accumulation and fill factor reduction; this can be mitigated by limiting the active layer thickness to 134–949 nm. Additionally, Tet-CdO exhibits inherently weak thermal dissipation, so device thinning, high-thermal-conductivity substrates, or active cooling are needed to suppress heat buildup. These findings establish Tet-CdO as a promising next-generation photovoltaic material.

Uncovering novel photoluminescence characteristics of Cu2ZnSnS4 thin-film solar cells through pulsed laser excitation

Photoluminescence (PL) spectroscopy under pulsed laser excitation was employed to investigate the recombination mechanisms in a Cu2ZnSnS4 (CZTS) thin-film solar cell over a temperature range of 8–300 K. The PL spectra revealed one asymmetric band at 1.27 eV at T = 8 K, which was successfully fitted using an asymmetric double sigmoidal shape, indicating spatial variations in localized states and bandgap fluctuations. The PL band exhibited a temperature-dependent blue shift (∼0.26 meV/K) and low thermal activation energy (∼22 meV), suggesting recombination involving closely spaced deep donor–deep acceptor pairs. Laser power-dependent PL measurements at 8 K showed a pronounced blue shift of approximately 31 meV per decade of laser power, attributed to a band-filling effect under high excitation densities. The results support a model in which recombination occurs near band-bending regions. This study highlights the sensitivity of pulsed laser excitation PL, revealing previously unresolved recombination dynamics and localized states in CZTS-based photovoltaic materials.

Observation of single antiferromagnetic magnon modes through tunneling spectroscopy of spin-1/2 Kitaev system α-RuCl3

The small-gap room-temperature semiconductor α-RuCl3, which is known to undergo a Mott-Hubbard transition at low temperatures, is one of the most promising candidates for realization of an exotic matter form, the quantum spin liquid state, which may have applications in quantum computing. Although extensively investigated by neutron scattering techniques, electronic study of this system in the form of van der Waals heterostructures has been limited mainly to graphene proximity. Here, we report a systematic study of planar and tunneling electronic properties of α-RuCl3 films, where we observe an n-type field effect on α-RuCl3 films at room temperature, with a Mott insulator nature onset below 120 K. For films of three-layer thickness and below, we find inelastic scattering features below the Néel temperature of 7–14.5 K, which we attribute to single-magnon modes. Our study confirms preserved low-temperature signatures of the zigzag antiferromagnetic order in the atomically thin limit and its single-magnon modes within the continuum through tunneling spectroscopy.

Single-shot ultrafast dynamics of nanosecond pulsed plasmas: Transition from ps–ns nonequilibrium to near-full ionization

The ultrafast multi-stage evolution of state-defining properties in atmospheric-pressure nanosecond pulsed plasmas is quantified using single-discharge, jitter-free, continuous streak-sweep spectroscopy of N2(C → B) molecular and N+/O+ ionic species with a single-shot time resolution as short as ∼160 ps. An early period of extreme nonequilibrium is observed with vibrational temperatures [TV(C)] dropping from ∼8000 K at &amp;lt;200 ps after plasma breakdown to &amp;lt;4000 K within ∼1 ns, with near-ambient rotational temperatures [TR(C)] ∼ 300 K due to limited collisional energy transfer. This early-time TV(C) trend is representative of a direct and unquenched look into the high-energy tail of the electron energy distribution function; thus, it tracks real-time changes in the mean electron energy via the N2(C) emission signatures. This is followed by the rapid onset of N+/O+ ionic emission after a distinct time delay of ∼14.9 ns due to multistep chemical kinetics. The ionic emission enables determination of electron densities (ne) &amp;gt;2 × 1019 cm−3 and electron temperatures (Te) &amp;gt;36 000 K, indicating the transition to a nearly fully ionized regime. The ps–ns temporal dynamics are also compared between air and N2 plasmas to assess the influence of collisional partners, as well as across the anode, cathode, and central gap regions to identify spatial variations in plasma behavior. This work demonstrates versatile continuously probing approach capable of spectro-temporal and spatially resolved single-shot measurements of key state variables in the ps–ns evolution of atmospheric-pressure nanosecond pulsed plasmas.

The hepatic FGFR-ERK-HRG axis regulates heparin-induced thrombocytopenia with thrombosis

Heparin-induced thrombocytopenia (HIT) is a life-threatening prothrombotic disorder with substantial clinical mortality, characterized by pathologic antibody formation against platelet factor 4 (PF4)-heparin complexes. This study identified early pathologic mechanisms that initiate HIT immune complex formation and regulate thrombosis development. We found that repeated heparin administration over five days markedly enhanced platelet activation which implies an additional activating mechanism. Through plasma proteomic analysis, we observed that histidine-rich glycoprotein (HRG) levels were significantly reduced following successive heparin administration, and inversely related to platelet activation. Mechanistically, heparin and PF4 suppressed HRG expression via inhibiting the FGFR-ERK-Elk1 pathway whereby Elk1 directly binds to the HRG promoter region to regulate its liver expression. Physiological levels of HRG potently inhibited platelet activation, procoagulant activity, spreading, and aggregation, and significantly reduced thrombus formation under flow conditions. HRG bound to activated αIIbβ3 integrin in a zinc-dependent manner, thereby blocking its ligand-binding capacity. HRG also inhibited the formation of ultralarge PF4-heparin complexes (ULCs), disrupted the immune complexes (ULICs) comprising the HIT-like antibody KKO and ULCs, and blocked the binding of KKO to PF4/heparin on platelets. Furthermore, HRG attenuated ULCs-triggered autoantibody generation, inhibited the ULICs-induced neutrophil extracellular traps and microvascular thrombosis formation both in vitro and in a mouse model of HIT. In conclusion, our work establishes HRG as a pivotal regulator of pathologic immune responses and thrombosis in HIT, providing mechanistic insights into disease pathogenesis.

Publisher's Note: “Pressure-induced contact resistance dominance in scanning spreading resistance microscopy of undoped InAs/GaSb heterostructure” [Appl. Phys. Lett. <b>128</b> , 262106 (2026)]

HOW I TREAT BLEEDING IN WOMEN AND GIRLS WITH HEMOPHILIA/ HEMOPHILIA CARRIERS

Historically the impact of hemophilia for female carriers was believed to be restricted to their male offspring. Recent studies have highlighted the increased bleeding experienced by many hemophilia carriers, challenging traditional concepts of X-linked inheritance. These data have resulted in a mindset shift in the haemostasis community, culminating in the 2021 ISTH update on classification of hemophilia carriers. Women and girls with reduced factor VIII (FVIII) /factor IX (FIX) levels &amp;lt;0.40 IU/mL are now recognised as women and girls with hemophilia (WGH). Furthermore, hemophilia carriers who experience excessive bleeding despite normal FVIII/FIX levels are termed symptomatic carriers. Despite these changes, the impact of historic misconceptions surrounding hemophilia carriership remains and many families and healthcare providers may still believe that hemophilia carriers are at no risk of increased bleeding. Education is key to address these ongoing challenges and engagement with both hemophilia communities and physician organisations is critical. Hemophilia treatment centers must endeavour to ensure access for all hemophilia carriers and availability of services appropriate to needs of hemophilia carriers and WGH throughout their lifespan. In contrast to past publications that focus on pregnancy, in this article we address bleeding in hemophilia carriers and WGH at different life stages, including the impact of delay on diagnosis and the management of reproductive tract and joint bleeding.

Experimental observation of metamaterial-enabled high-density waveguides with low crosstalk

Crosstalk in densely spaced waveguides fundamentally constrains the integration density of photonic circuits. Although various strategies exist to mitigate crosstalk for transverse-electric (TE) modes, suppressing transverse-magnetic (TM) mode crosstalk remains challenging due to the weaker optical confinement of TM modes. Here, we address this challenge by introducing an anisotropic metamaterial between waveguide cores and the substrate, which effectively suppresses TM-mode crosstalk and enables dense waveguide integration. This mechanism is confirmed through both proof-of-principle microwave experiments and numerical simulations of on-chip silicon strip waveguides. We show that with a center-to-center separation of 1200 nm—nearly half the distance required by conventional waveguides—the designed silicon strip waveguides exhibit crosstalk below −20 dB for both fundamental TM and TE modes across a broad wavelength range from 1440 to 1555 nm. Our approach not only enhances the performance and integration compatibility of TM-mode-based photonic devices but also provides a viable pathway toward ultracompact, polarization-multiplexed integrated photonic circuits.

Measurable Residual Disease-Dependent Unfavorable Outcomes in Pediatric PAX5-Rearranged B-Acute Lymphoblastic Leukemia

PAX5-altered acute lymphoblastic leukemia (PAX5-alt ALL) is a recently recognized molecular subtype of B-ALL characterized by a distinct transcriptional signature and frequent PAX5 fusions (PAX5-r). While PAX5-alt ALL has been associated with intermediate outcomes, clinical data specifically investigating pediatric PAX5-r ALL remain limited. We collected and analyzed 159 pediatric cases of PAX5-r ALL treated between 2001-2024 within AIEOP-BFM ALL studies across Italy, Germany and Austria, revealing high-risk clinical features. Comparative analyses of patients consecutively enrolled in the AIEOP-BFM ALL 2017 study (PAX5-r, n=96 vs. non-PAX5-r, n=1948) confirmed higher rates of hyperleukocytosis at diagnosis (22.9% vs. 8%, p&amp;lt;0.001) and enrichment of IKZF1plus profile (14.7% vs. 7.8%, p=0.0015) in PAX5-r patients. No relevant differences in terms of minimal/measurable residual disease (MRD)-based treatment response and risk-group stratification were observed. PAX5-r patients had a 4-year EFS and OS of 72.6±5.7% and 95.4±2.3%, respectively. Four-year EFS were 100%, 63.4±9.7% and 63.3±10% for standard-risk, medium-risk (MR) and high-risk (HR) groups, respectively, indicating that the poor prognostic impact of PAX5-r applies only when end-of-induction MRD is positive (MR/HR). Whole transcriptome sequencing revealed high FLT3 median expression in PAX5-r ALL and high-throughput drug screening of patient-derived xenografts (PDXs) showed marked sensitivity to several FLT3 inhibitors. Gilteritinib showed potent ex vivo cytotoxicity and synergism with dexamethasone in PAX5-r PDX models. Collectively, this study investigated clinical and biological features of pediatric PAX5-r ALL highlighting its MRD-dependent unfavorable prognosis and identifying FLT3 overexpression as a novel, potential therapeutic target.

Splitting and merging behaviors of the positive streamer propagating in an atmospheric pressure argon plasma jet

Atmospheric pressure plasma jet (APPJ) offers extensive potential applications and has become a hot topic in low-temperature plasma research. The streamer dynamics are crucial to the distribution of reactive species in APPJ. To shed light on the streamer dynamics, the behaviors of splitting and merging are reported in this work for the positive streamer propagating in an argon APPJ. Results indicate that two discharges (the negative and the positive streamers) occur at the voltage rising edge and the falling edge, respectively. Their discharge intensities vary with changing pulse amplitude (Va) and bias voltage (Vb). High-speed photography reveals that the track of the positive streamer is filamentary, whose structure evolves with increasing Va from a cone, a fork, and to a fork and void. Additionally, the fork-and-void structure becomes a two-void shape with decreasing Vb. Moreover, the positive streamer demonstrates various behaviors, including linear propagation, splitting, merging, double splitting, and double merging. Spatial distributions of streamer velocity, electron excitation temperature, electron density, and molecular vibration temperature are also investigated. It is deduced that splitting and re-splitting are attributed separately to the negative ions and the Penning effect in the interfacial layer. If the negative ions in the interfacial layer are insufficient or the Penning effect at the axis is strong enough, merging and re-merging occur, respectively. The results mentioned above are of great significance for improving the performance of APPJ.

FERMT3 alternative splicing enhances kindlin-3 membrane recruitment for neutrophil adhesion during stress myelopoiesis

Leukocyte Adhesion Deficiency syndrome type III (LAD-III) is characterized by recurrent infections and is caused by FERMT3 gene mutations. FERMT3 encodes two isoforms, a standard kindlin-3 and a longer splicing variant, which differs by the addition of four residues Ile-Pro-Arg-Arg (IPRR) in the pleckstrin homology (PH) domain (kindlin-3-IPRR). Previous studies suggested that kindlin-3-IPRR was dysfunctional in inducing neutrophil adhesion, attributed to altered phospholipid binding of the IPRR-containing PH domain. Here we show that kindlin-3-IPRR is fully functional in activating β2 integrins and promotes neutrophil adhesion. The IPRR insert enhances phospholipid binding in vitro and promotes association of kindlin-3 with the plasma membrane. By analyzing RNA sequencing datasets of neutropoiesis, we show that the kindlin-3 short isoform lacking IPRR is highly expressed in neutrophil precursors but downregulated in mature neutrophils. In contrast, a higher proportion of the long isoform was detected in hematopoietic stem cells (HSCs) and mature neutrophils. Kindlin-3-IPRR supports robust adhesion of HSCs. We propose that kindlin-3-IPRR may be crucial in conditions requiring rapid neutrophil mobilization. Indeed, kindlin-3 splicing is altered in neutrophils from patients undergoing stress myelopoiesis after exposure to granulocyte colony-stimulating factor (G-CSF) or HSC transplantation (HSC-T) compared with healthy donors. During stress myelopoiesis induced by G-CSF treatment, the kindlin-3 long isoform is selectively upregulated in mature neutrophils, coinciding with enhanced β2 integrin activation. These findings support a model in which alternative splicing of FERMT3 dynamically fine-tunes integrin activation and leukocyte adhesion during hematopoietic stress, with potential implications for monitoring hematopoietic recovery after HSC transplantation.

Radiation force alignment for accurate orbital angular momentum measurement in acoustic vortex beams

We introduce a hologram-based method to determine the physically optimal axis for measuring the orbital angular momentum (OAM) transferred by acoustic vortex beams to an absorbing target. The axis is aligned with the net radiation force vector obtained from holographically measured pressure field. This alignment eliminates the transverse force component, making the measured torque independent of lateral position and equal to the OAM flux. The method is validated with vortex beams generated by multi-sector phase plates on a planar transducer and significantly improves upon conventional geometric alignment for nonparaxial and aberrated beams.