arXiv subjects

Pushpendra Yadav

Publications and source records attributed to Pushpendra Yadav.

7 recordsLinked to original sources

arXiv2026

Observation of Time-Reversal Symmetry Breaking in the Type-I Superconductor YbSb$_2$

The spontaneous breaking of time-reversal symmetry is a hallmark of unconventional superconductivity, typically observed in type-II superconductors. Here, we report evidence of time-reversal symmetry breaking in the type-I superconductor YbSb$_2$. Zero-field $\mu$SR measurements reveal spontaneous internal magnetic fields emerging just below the superconducting transition, while transverse-field $\mu$SR confirms a fully gapped type-I superconducting state. Our first-principles calculations identify YbSb$_2$ as a ${\mathbb Z}_2$ topological metal hosting a Dirac nodal line near the Fermi level. Symmetry analysis within the Ginzburg Landau framework indicates an internally antisymmetric nonunitary triplet (INT) state as the most probable superconducting ground state. Calculations based on an effective low-energy model further demonstrate that this INT state hosts gapless Majorana surface modes, establishing YbSb$_2$ as a topological superconductor. Our results highlight YbSb$_2$ as a unique material platform where type-I superconductivity coexists with triplet-pairing and nontrivial topology.

cond-mat.supr-con↗

arXiv2025

Exciton dynamics in equilibrium and nonequilibrium regimes

The bound electron-hole pairs known as excitons govern the optical properties of insulating solids. While their behavior in equilibrium is well-understood theoretically, the nonequilibrium regime at high excitation densities-where phenomena like electron-hole liquids emerge - is less explored. This thesis presents a first-principles study of excitons in two-dimensional materials. We use the GW approximation and the Bethe-Salpeter equation to investigate their properties from equilibrium to nonequilibrium conditions. We first demonstrate how increasing photo-excited carrier density leads to a redshift-blueshift crossover of excitons. We then show that electron-phonon interactions critically modify optical spectra and exciton lifetimes at finite temperatures. Finally, we unify these effects to demonstrate the formation of an electron-hole liquid phase above a critical carrier density and below a critical temperature. Our work identifies how enhanced Coulomb interactions in two dimensions can stabilize this phase at significantly higher temperatures, proposing promising material candidates for observing these collective states.

cond-mat.mes-hall↗

arXiv2024

Phonon-Assisted Photoluminescence and Exciton Recombination in Monolayer Aluminum Nitride

Efficient solid-state photon emitters with longer operating lifetimes in the ultraviolet (UV) wavelength range are crucial for optoelectronic devices. However, finding suitable material candidates has been a significant challenge. Here, we demonstrate that hexagonal aluminum nitride (AlN) monolayers exhibit strong photoluminescence emission within the UV range of 3.94 - 4.05 eV. We show that these emissions in indirect bandgap AlN are facilitated by phonon modes with finite lattice momentum. These phonon modes promote efficient recombination of electrons and holes from the $\Gamma$ to K point of the Brillouin zone. Our findings provide a foundation for developing advanced optoelectronic devices and efficient UV light sources based on hexagonal AlN monolayers.

cond-mat.mes-hall↗

arXiv2023

Room temperature electron-hole liquid phase in monolayer MoSi$_2$Z$_4$ (Z = pinctogen)

Photo-excited electrons and holes in insulators, above a critical density and below a critical temperature, can condense to form an electron-hole liquid (EHL) phase. However, observing the EHL phase at room temperature is extremely challenging. Here, we introduce the monolayer MoSi$_2$Z$_4$ (Z= N, As, P) series of compounds as a promising platform for observing the EHL phase at room temperature. The higher impact of the Coulomb interactions in two dimensions helps these monolayers support the EHL phase with an increased EHL binding energy and transition temperature, along with strongly bound excitons. Our findings motivate further exploration of the MoSi$_2$Z$_4$ monolayers for realizing the EHL phase at high temperatures to harness collective phenomena for optoelectronic applications.

cond-mat.mes-hall↗

arXiv2023

Room Temperature Ferroelectricity, Ferromagnetism, and Anomalous Hall Effect in Half-metallic Monolayer CrTe

Two-dimensional materials hosting ferroelectricity and ferromagnetism are crucial for low-power and high-speed information processing technologies. However, intrinsic 2D multiferroics in the monolayer limit are rare. Here, we demonstrate that monolayer CrTe, obtained by cleaving the [002] surface, is dynamically stable multiferroic at temperatures beyond room temperature. We show that it orders ferromagnetically with significant in-plane magnetocrystalline anisotropy, and it is a half-metal featuring a large half-metal gap. Remarkably, the broken inversion symmetry and buckled geometry of monolayer CrTe make it a ferroelectric with a large spontaneous out-of-plane polarization and significant magnetoelectric coupling. In addition, we demonstrate polarization or electric field-induced tunability of the anomalous Hall effect, accompanied by substantial bandstructure modulation. Our findings establish monolayer CrTe as a room-temperature multiferroic with great potential for applications in spintronics and ferroelectric devices.

cond-mat.mes-hall↗

arXiv2022

Strongly bound excitons in monolayer MoSi$_2$Z$_4$ (Z = pnictogen)

Reduced dielectric screening in two-dimensional materials enables bound excitons, which modifies their optical absorption and optoelectronic response even at room temperature. Here, we demonstrate the existence of excitons in the bandgap of the monolayer family of the newly discovered synthetic MoSi$_2$Z$_4$ (Z = N, P, and As) series of materials. All three monolayers support several bright and strongly bound excitons with binding energies varying from 1 eV to 1.35 eV for the lowest energy exciton resonances. On increasing the pump fluence, the exciton binding energies get renormalized, leading to a redshift-blueshift crossover. Our study shows that the MoSi$_2$Z$_4$ series of monolayers offer an exciting test-bed for exploring the physics of strongly bound excitons and their non-equilibrium dynamics.

cond-mat.mes-hall↗

arXiv2021

Competing magnetic interactions and magnetocaloric effect in Ho$_5$Sn$_3$

The rare-earth intermetallic compound Ho$_5$Sn$_3$ demonstrates fascinating magnetic properties which include temperature-driven multiple magnetic transitions and field driven metamagnetism. We address the magnetic character of this exciting compound through a combined experimental and theoretical studies. Ho$_5$Sn$_3$ orders antiferromagnetically below $~28$ K, and shows further spin reorientation transitions at 15 K and 12 K. We observe a sizable amount of low-temperature magnetocaloric effect in Ho$_5$Sn$_3$ with a maximum value of entropy change $\Delta S$ = -9.5 JKg$^{-1}$K$^{-1}$ for an applied field of $H$ = 50 kOe at around 30 K. The field hysteresis is almost zero above 15 K where magneto-caloric effect is important. Interestingly, $\Delta S$ is found to change its sign from positive to negative as the temperature is increased above about 8 K, which can be linked to the multiple spin reorientation transitions. The signature of the metamagnetism is visible in the $\Delta S$ versus $H$ plot. The magnetic ground-state, obtained from the density functional theory based calculation, is susceptible to the effective Coulomb interaction ($U_{\rm eff}$) between electrons. Depending upon the value of $U_{\rm eff}$, the ground-state can be ferromagnetic or antiferromagnetic. The compound shows large relaxation (14\% change in magnetization in 60 min) in the field cooled state with a logarithmic time variation, which may be connected to the competing magnetic ground-states observed in our theoretical calculations. The competing magnetic ground-states is also evident from the small value of the paramagnetic Curie-Weiss temperature.

cond-mat.str-el↗