arXiv subjects

Satya K. Kushwaha

Publications and source records attributed to Satya K. Kushwaha.

15 recordsLinked to original sources

arXiv2026

Enabling the Ambient Pressure Growth of ScB2 Crystals for AlGaN Power Electronics

Here we report the growth of single crystalline ScB2, an ultrahigh-temperature ceramic, at ambient pressure in a laser-heated Optical Floating Zone via the travelling solvent method. Crystals have been grown from both Sc-rich (55-65 at% Sc) and B-rich self-flux (80-83 at% B) at growth rates in the range of 0.2-2 mm/hr. The structure of grown crystals is in good agreement with an AlB2-type layered hexagonal phase, space group P6/mmm, with lattice constants a = 3.1423(2) Å (resp. 3.1502(3) Å) and c = 3.5084(3) Å (resp. 3.5041(3) Å) for crystals grown under Sc-rich (resp. B-rich) conditions. Crystals natively grow along the in-plane [100] direction. Electron backscattered diffraction shows that Sc-flux growth results in boules with multiple domains containing Sc inclusions, with the domains highly aligned. In contrast, B-flux boules are single domain after the initial nucleation region. Rocking-curve measurements of B-flux crystals for the (h000) and (000l) reflections show single peaks, establishing that the crystals are free from grain boundaries; the asymmetry in the scattered-intensity tails suggests the presence of point defects. Surface X-ray photoemission spectroscopy shows that the electronic environment in B-flux crystals is superior to that of Sc-flux crystals and produces highly resolved binding-energy peaks for B 1s and Sc 2p. Work-function measurements for the (11-20) plane give a value of approximately 5 eV, consistent with the highly electrically conductive nature of ScB2. These results demonstrate the viable ambient-pressure growth of ScB2, establish it as a lattice-matched substrate candidate for Al-rich AlGaN power microelectronics, and show that this growth route enables scalable manufacturing of ScB2 substrates.

cond-mat.mtrl-sci↗

arXiv2026

Crystal growth and characterization of the ultra-high temperature substrate $\mathrm{Ta_{1-x}Hf_{x}C_{0.5}}$

Incorporation of $\mathrm{Al_{y}Ga_{1-y}N}$ (AGN) semiconductors into high power electronics offers efficiency improvements in power transmission, generation, and use, if approaches to eliminate the defects arising from film-lattice mismatch can be established. Here, we report the optical floating zone crystal growth of $\mathrm{Ta_{1-x}Hf_{x}C_{0.5}}$ (x = 0.2), a new metallic substrate material family lattice matched to the ultra-wide-band-gap, Al-rich side (y = 0.91) of the AGN solid solution. Laue diffraction demonstrates large single crystal domains in the as-grown boule. Single crystal x-ray diffraction at T = 213 K in conjunction with first principles calculations shows that the material adopts a layered crystal structure with AA-type stacking of (Ta/Hf)-C-(Ta/Hf) trilayers described in the trigonal space group P-3m1 (#164), with a = 3.1168(4) Å, c = 4.9644(4) Å, and $β$ = 120.0°. X-ray photoelectron spectroscopy (XPS) measurements show the Hf:Ta ratio to be close to the nominal value of 0.8:0.2 in the grown crystal. Density Functional Theory calculations reveal that this structure is stabilized by the low energy of carbon-vacancy formation of a hypothetical $\mathrm{(Ta/Hf)_{1}C_{1}}$ anti-NiAs structure type, and imply flexibility in interface structure with an overlayer nitride film. A surface preparation/polishing procedure is developed that reduces root mean square (RMS) surface roughness from as-cut 130 nm to 7 nm as measured by atomic force microscopy. Scanning electron microscopy shows the presence of a native surface oxide, removed by polishing, along with carbon-rich pits. Time-domain thermoreflectance measurements show a room temperature thermal conductivity of $κ$ = 18.1(4) W m-1 K-1. These results provide key first steps for utilizing metallic, lattice matched, substrates for the growth of Al-rich AGN semiconductors.

cond-mat.mtrl-sci↗

arXiv2026

Vortex-parity-controlled diode effect in Corbino topological Josephson junctions

Nonreciprocal supercurrents in Josephson junctions have recently emerged as a sensitive tool for investigating broken symmetries in superconducting quantum materials. Here, we report an even-odd Josephson diode effect (JDE) in Corbino-geometry junctions fabricated on the pristine surface of a bulk-insulating three-dimensional topological insulator (3DTI). We find that the diode polarity, which indicates the preferred direction of supercurrent flow, robustly alternates its sign depending on the parity (even or odd) of the enclosed vortex number. This behavior is absent in two key control devices: a non-topological graphene Corbino Josephson junction and a 3DTI-based linear Josephson junction. These results indicate that the polarity-tunable JDE is intrinsically linked to the unique combination of the proximitized topological superconductivity in the 3DTI surface and the Corbino device's closed-loop geometry. Our theoretical modeling attributes the observed sign change in diode polarity to the alternating sign of periodic boundary conditions in topological superconductors, supporting the interpretation that the vortex-parity-controlled JDE is a direct manifestation of the underlying Andreev bound state topology associated with the presence of non-Abelian anyons in the vortices.

cond-mat.supr-con↗

arXiv2025

Surface-dominant transport in Weyl semimetal NbAs nanowires for next-generation interconnects

Ongoing demands for smaller and more energy efficient electronic devices necessitate alternative interconnect materials with lower electrical resistivity at reduced dimensions. Despite the emergence of many promising candidates, synthesizing high quality nanostructures remains a major bottleneck in evaluating their performance. Here, we report the successful synthesis of Weyl semimetal NbAs nanowires via thermomechanical nanomolding, achieving single crystallinity and controlled diameters as small as 40 nm. Our NbAs nanowires exhibit a remarkably low room-temperature resistivity of 9.7 +/- 1.6 microOhm-cm, which is three to four times lower than their bulk counterpart. Theoretical calculations corroborate the experimental observations, attributing this exceptional resistivity reduction to surface dominant conduction with long carrier lifetime at finite temperatures. Further characterization of NbAs nanowires and bulk single crystals reveals high breakdown current density, robust stability, and superior thermal conductivity. Collectively, these properties highlight the strong potential of NbAs nanowires as next-generation interconnects, which can surpass the limitations of current copper-based interconnects. Technologically, our findings present a practical application of topological materials, while scientifically showcasing the fundamental properties uniquely accessible in nanoscale platforms.

cond-mat.mes-hall↗

arXiv2023

The Reverse Quantum Limit: Implications for Unconventional Quantum Oscillations in YbB$_{12}$

Beyond the quantum limit, many-body effects are expected to induce unusual electronic phase transitions. Materials possessing metallic ground states with strong interactions between localized and itinerant electronic states are natural candidates for the realization of such quantum phases. However, the electronic correlations responsible for increasing the likelihood of novel phases simultaneously place the quantum limit beyond the reach of laboratory magnets. Here we propose these difficulties can be surmounted in materials with strong correlations and insulating ground states. Strong correlations in insulators and high magnetic fields conspire to fill Landau levels in the reverse order compared to conventional metals, such that the lowest Landau level is the first observed. Consequently, the quantum limit in strongly correlated insulators is reached in reverse and at fields accessible in laboratories. Quantum oscillations measured at high fields in YbB12 are shown to have features consistent with the reverse quantum limit. These include how quantum oscillations move in lock step with the angular evolution of the insulator-metal transition and the field dependence of the quantum oscillation frequency. We argue that close to the insulator-metal transition, the insulating state should be viewed through the lens of a magnetic field-induced electronic instability affecting the lowest Landau level states in the quantum limit.

cond-mat.str-el↗

arXiv2019

Magnetic field-tuned quantum criticality in a Kondo insulator

Kondo insulators are predicted to undergo an insulator-to-metal transition under applied magnetic field, yet the extremely high fields required to date have prohibited a comprehensive investigation of the nature of this transition. Here we show that Ce3Bi4Pd3 provides an ideal platform for this investigation, owing to the unusually small magnetic field of B ~ 11 T required to overcome its Kondo insulating gap. Above Bc, we find a magnetic field-induced Fermi liquid state whose characteristic energy scale T_FL collapses near Bc in a manner indicative of a magnetic field-tuned quantum critical point. A direct connection is established with the process of Kondo singlet formation, which yields a broad maximum in the magnetic susceptibility as a function of temperature in weak magnetic fields that evolves progressively into a sharper transition at Bc as T -> 0.

cond-mat.str-el↗

arXiv2017

Realization of a Type-II Nodal-Line Semimetal in Mg$_3$Bi$_2$

Nodal-line semimetals (NLSs) represent a new type of topological semimetallic beyond Weyl and Dirac semimetals in the sense that they host closed loops or open curves of band degeneracies in the Brillouin zone. Parallel to the classification of type-I and type-II Weyl semimetals, there are two types of NLSs. The conventional NLS phase, in which the two bands forming the nodal line have opposite signs for their slopes along any direction perpendicular to the nodal line, has been proposed and realized in many compounds, whereas the exotic type-II NLS is very rare. Our first-principles calculations show that Mg$_3$Bi$_2$ is a material candidate that hosts a single type-II nodal loop around $Γ$. The band crossing is close to the Fermi level and the two crossing bands have the same sign in their slopes along the radial direction of the loop, indicating the type-II nature of the nodal line. Spin-orbit coupling generates only a small energy gap ($\sim$35 meV) at the nodal points and does not negate the band dispersion of Mg$_3$Bi$_2$ that yields the type-II nodal line. Based on this prediction we have synthesized Mg$_3$Bi$_2$ single crystals and confirmed the presence of the type-II nodal lines in the material. Our angle-resolved photoemission spectroscopy (ARPES) measurements agree well with our first-principles results and thus establish Mg$_3$Bi$_2$ as an ideal materials platform for studying the exotic properties of type-II nodal line semimetals.

cond-mat.mtrl-sci↗

arXiv2017

Anisotropic magnetic properties of the ferromagnetic semiconductor CrSbSe$_3$

Single crystals of CrSbSe$_3$, a structurally pseudo-one-dimensional ferromagnetic semiconductor, were grown using a high-temperature solution growth technique and were characterized by x-ray diffraction, anisotropic, temperature- and field-dependent magnetization, temperature-dependent resistivity and optical absorption measurements. A band gap of 0.7 eV was determined from both resistivity and optical measurements. At high temperatures, CrSbSe$_3$ is paramagnetic and isotropic with a Curie-Weiss temperature of $\sim$145 K and an effective moment of $\sim$4.1 $μ_B$/Cr. A ferromagnetic transition occurs at $T_c$ = 71 K. The $a$-axis, perpendicular to the chains in the structure, is the magnetic easy axis, while the chain axis direction, along $b$, is the hard axis. Magnetic isotherms measured around $T_c$ do not follow the behavior predicted by simple mean field critical exponents for a second order phase transition. A tentative set of critical exponents is estimated based on a modified Arrott plot analysis, giving $β\sim$0.25, $γ\sim$1.38 and $δ\sim$6.6.

cond-mat.mtrl-sci↗

arXiv2017

Growth, Crystal Structure and Magnetic Characterization of Zn-Stabilized CePtIn4

The growth and characterization of CePtIn4, stabilized by 10% Zn substitution for In, is reported. The new material is orthorhombic, space group Cmcm (No. 63), with lattice parameters a = 4.51751(4) Å, b = 16.7570(2) Å, and c = 7.36682(8) Å, and the refined crystal composition has 10% of Zn substituted for In, i.e. the crystals are CePt(In3.6Zn0.1)4. Crystals were grown using a self-flux method: only growths containing Zn yielded CePtIn4 crystals, while Ce3Pt4In13 crystals formed when Zn was not present. Anisotropic temperature-dependent magnetic susceptibilities for single crystals show that Zn-stabilized CePtIn4 orders magnetically at ~1.9 K. High-temperature Curie-Weiss fits indicate an effective moment of ~2.30 muB/ Ce and a directionally averaged Weiss-temperature of approximately - 9 K. Specific heat data shows a peak consistent with the ordering temperature seen in the magnetic susceptibility data. Zn-stabilized CePtIn4 is metallic and displays no superconducting transition down to 0.14 K.

cond-mat.mtrl-sci↗

arXiv2016

Imaging electronic states on topological semimetals using scanning tunneling microscopy

Following the intense studies on topological insulators, significant efforts have recently been devoted to the search for gapless topological systems. These materials not only broaden the topological classification of matter but also provide a condensed matter realization of various relativistic particles and phenomena previously discussed mainly in high energy physics. Weyl semimetals host massless, chiral, low-energy excitations in the bulk electronic band structure, whereas a symmetry protected pair of Weyl fermions gives rise to massless Dirac fermions. We employed scanning tunneling microscopy/spectroscopy to explore the behavior of electronic states both on the surface and in the bulk of topological semimetal phases. By mapping the quasiparticle interference and emerging Landau levels at high magnetic field in Dirac semimetals Cd$_3$As$_2$ and Na$_3$Bi, we observed extended Dirac-like bulk electronic bands. Quasiparticle interference imaged on Weyl semimetal TaAs demonstrated the predicted momentum dependent delocalization of Fermi arc surface states in the vicinity of the surface-projected Weyl nodes.

cond-mat.mtrl-sci↗

arXiv2016

Superconductivity in CaBi$_{2}$

Superconductivity is observed with critical temperature $T_{c}$ = 2.0 K in self-flux-grown single crystals of $CaBi_{2}$. This material adopts the $ZrSi_{2}$ structure type with lattice parameters a = 4.696(1) $Å$, b = 7.081(2) $Å$ and c = 4.611(1) $Å$. The crystals of $CaBi_{2}$ were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at $T_{c}$ is $ΔC/γT_{c}$ = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient $γ$ = 4.1 $mJ\: mol^{-1}\, K^{-2}$ and the Debye temperature $Θ_{D}$ = 157 K. The electron-phonon coupling strength is $λ_{el-ph}$ = 0.59, and the thermodynamic critical field $H_{c}$ is low, between 111 and 124 Oe $CaBi_{2}$ is a moderate coupling type-I superconductor. Results of electronic structure calculations are reported and charge densities, electronic bands, densities of states and Fermi surfaces are discussed, focusing on the effects of spin\textendash orbit coupling and electronic property anisotropy. We find a mixed quasi-2D + 3D character in the electronic structure, which reflects the layered crystal structure of the material.

cond-mat.supr-con↗

arXiv2016

A new form of (unexpected) Dirac fermions in the strongly-correlated cerium monopnictides

Discovering Dirac fermions with novel properties has become an important front in condensed matter and materials sciences. Here, we report the observation of unusual Dirac fermion states in a strongly-correlated electron setting, which are uniquely distinct from those of graphene and conventional topological insulators. In strongly-correlated cerium monopnictides, we find two sets of highly anisotropic Dirac fermions that interpenetrate each other with negligible hybridization, and show a peculiar four-fold degeneracy where their Dirac nodes overlap. Despite the lack of protection by crystalline or time-reversal symmetries, this four-fold degeneracy is robust across magnetic phase transitions. Comparison of these experimental findings with our theoretical calculations suggests that the observed surface Dirac fermions arise from bulk band inversions at an odd number of high-symmetry points, which is analogous to the band topology which describes a $\mathbb{Z}_{2}$-topological phase. Our findings open up an unprecedented and long-sought-for platform for exploring novel Dirac fermion physics in a strongly-correlated semimetal.

cond-mat.str-el↗

arXiv2015

Signature of the chiral anomaly in a Dirac semimetal: a current plume steered by a magnetic field

In this talk, we describe recent experimental progress in detecting the chiral anomaly in the Dirac semimetal Na$_3$Bi in the presence of a magnetic field. The chiral anomaly, which plays a fundamental role in chiral gauge theories, was predicted to be observable in crystals by Nielsen and Ninomiya in 1983 [1]. Theoretical progress in identifying and investigating Dirac and Weyl semimetals has revived strong interest in this issue [2-6]. In the Dirac semimetal, the breaking of time-reversal symmetry by a magnetic field $\bf B$ splits each Dirac node into two chiral Weyl nodes. If an electric field $\bf E$ is applied parallel to $\bf B$, charge is predicted to flow between the Weyl nodes. We report the observation in the Dirac semimetal Na$_3$Bi of a novel, negative and highly anisotropic magnetoresistance (MR). We show that the enhanced conductivity has the form of a narrowly defined plume that can be steered by the applied field. The novel MR is acutely sensitive to deviations of $\bf B$ from $\bf E$, a feature incompatible with conventional transport. The locking of the current plume to the field appears to be a defining signature of the chiral anomaly.

cond-mat.str-el↗

arXiv2015

Observation of Fermi Arc Surface States in a Topological Metal: A New Type of 2D Electron Gas beyond Z2 Topological Insulators

In a topological insulator, it is the electrons on the surface or edge that carry the signature of topology. Recently, a novel topological state has been proposed in metals or semimetals (gapless) whose band-structure is similar to that of a three-dimensional analog of graphene. However, to this date the signature of its topology remains an open question. We report the experimental discovery of a pair of polarized Fermi arc surface state modes in the form of a new type of two-dimensional polarized electron gas on the surfaces of Dirac semimetals. These Fermi arc surface states (FASS) are observed to connect across an even number of bulk band gapless nodes and found to have their spin uniquely locked to their momentum. We show that these states are distinctly different from the topological surface states (TSS) seen in all known topological insulators. Our observed exotic two-dimensional states not only uncover the novel topology of gapless Dirac metals (such as sodium tribismuth Na$_3$Bi) but also opens new research frontiers for the utilization of topological Fermi arc electron gases for a wide range of fundamental physics and spintronic studies.

cond-mat.mes-hall↗

arXiv2015

Bulk crystal growth and electronic characterization of the 3D Dirac Semimetal Na3Bi

High quality hexagon plate-like Na3Bi crystals with large (001) plane surfaces were grown from a molten Na flux. The freshly cleaved crystals were analyzed by low temperature scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), allowing for the characterization of the three-dimensional (3D) Dirac semimetal (TDS) behavior and the observation of the topological surface states. Landau levels (LL) were observed, and the energy-momentum relations exhibited a linear dispersion relationship, characteristic of the 3D TDS nature of Na3Bi. In transport measurements on Na3Bi crystals the linear magnetoresistance and Shubnikov-de Haas (SdH) quantum oscillations are observed for the first time.

cond-mat.str-el↗