arXiv subjects

Abhiram Soori

Publications and source records attributed to Abhiram Soori.

At least 19 recordsLinked to original sources

arXiv2026

Electrically controlled spin-splitting and asymmetric tunnel magnetoresistance in anti-altermagnets

Anti-altermagnets (AAMs) are a recently identified class of layered magnetic materials where opposite spin-splitting in adjacent layers creates a globally spin-degenerate band structure, rendering conventional spectroscopic detection highly difficult. In this paper, we theoretically demonstrate an all-electrical method to manipulate and probe this hidden magnetic order using a dual-gated transport junction. By applying a perpendicular displacement field, we break the spatial inversion symmetry of the lattice, explicitly lifting the global spin degeneracy. We attach ferromagnetic (FM) leads on either side of the AAM. Using quantum transport calculations, we show that this gate-induced spin-splitting manifests as a strongly asymmetric tunnel magnetoresistance (TMR) as a function of the lead magnetization. We identify specific crystallographic orientations where the TMR retains its symmetry despite the fully split bands, a direct consequence of exact momentum-space compensation. We further reveal that Rashba spin-orbit coupling guarantees robust, highly directional transport asymmetries even in the absence of an explicit chemical potential mismatch between the layers. Our findings establish a clear, electrically tunable framework for exploiting AAMs in next-generation spintronic architectures.

cond-mat.mes-hall↗

arXiv2026

Topologically protected perfect crossed Andreev reflection in flux-engineered quantum wire junctions

Generating non-locally entangled electron pairs via Cooper-pair splitting is vital for solid-state quantum information processing. However, isolating the underlying crossed Andreev reflection (CAR) is challenging due to competing transport processes like electron tunneling (ET) and local Andreev reflection (AR). Here, we propose a flux-tunable four-terminal normal metal-superconductor junction that achieves deterministic, 100\% efficient CAR. We demonstrate that at exactly half a magnetic flux quantum ($ϕ=π$), exact destructive Aharonov-Bohm and Peierls interferences structurally forbid ET and AR respectively. By tuning the central junction hopping, electron reflection is also suppressed to zero. Using the Cauchy argument principle, we prove that this suppression manifests as a quantized topological winding number, guaranteeing a topologically protected unit CAR probability. We establish that this regime is characterized by a strictly positive cross-correlation shot noise, providing an unambiguous experimental signature of Cooper-pair splitting. Furthermore, this perfect CAR is nearly broadband within the superconducting gap and remarkably robust against structural disorder, offering a highly resilient architecture for deterministic nonlocal entanglement generation.

cond-mat.mes-hall↗

arXiv2026

Josephson effect in bipolar magnetic semiconductors

We theoretically investigate equilibrium currents in a one-dimensional Josephson junction incorporating a bipolar magnetic semiconductor (BMS). We show that the intrinsic exchange splitting of the spin-resolved bands enables purely electrical control of the $0$--$π$ transition through gate-tunable modulation of the BMS chemical potential, eliminating the need for an external magnetic field. This provides a viable route toward electrically tunable $π$-junction behavior and highlights the potential of BMS-based Josephson devices for phase-controllable superconducting electronics. Furthermore, in the presence of Rashba spin--orbit coupling, we find an anomalous Josephson effect characterized by a finite equilibrium supercurrent at zero phase difference. This behavior originates from the intrinsic breaking of time-reversal symmetry associated with the spin-polarized electronic structure of the BMS. Interestingly, despite the simultaneous breaking of time-reversal and inversion symmetries---conditions often associated with nonreciprocal superconducting transport---we do not observe a Josephson diode effect. Our results therefore highlight an important distinction between anomalous Josephson transport and superconducting nonreciprocity: the former does not necessarily imply a finite critical-current asymmetry between opposite current directions.

cond-mat.supr-con↗

arXiv2026

Topological zero-reflection points in multi-terminal quantum wire junctions

We study scattering in noninteracting multi-terminal quantum wire junctions and show that junctions with dihedral symmetry can exhibit exact zero-reflection points for $N \ge 4$ terminals. By analyzing the scattering matrix, we identify these reflectionless points in the $(E,t')$ parameter space, where $E$ is the incident particle energy and $t'$ is the junction hopping amplitude. These points exhibit an even-odd dependence on $N$ and converge asymptotically to a common limiting value in the large-$N$ limit. We show that the reflectionless points are characterized by an integer winding number associated with the phase of the reflection amplitude, providing a topological description for their stability against weak on-site disorder. We also consider junctions with broken time-reversal symmetry and find that a magnetic flux can induce additional reflectionless points, including for the $N = 3$ case. For a four-terminal junction threaded by a $π$-flux, we identify a unique parameter regime in which the reflection amplitude vanishes over the entire energy band. Finally, we discuss experimental signatures through the behavior of Friedel oscillations and examine the stability of these reflectionless points in the presence of weak interactions.

cond-mat.mes-hall↗

arXiv2026

Nonreciprocal transverse currents in Rashba metal junctions under out-of-plane Zeeman fields

We study charge transport across a junction between a normal metal and a Rashba metal in the presence of a Zeeman field applied to the spin--orbit coupled region. While an out-of-plane Zeeman field does not generate a transverse response in a homogeneous Rashba system, we show that such a junction exhibits a finite transverse conductivity that is inherently nonreciprocal, i.e., it depends on the direction of the applied bias. We demonstrate that this effect originates from the breaking of the $k_y \to -k_y$ symmetry of the Hamiltonian in the presence of the Zeeman field, which prevents cancellation of transverse current contributions from opposite transverse momenta. We further show that evanescent modes in the spin--orbit coupled region play a crucial role by carrying a finite spin polarization that gives rise to a transverse current localized near the junction. The transverse conductivity exhibits a peak at an energy scale set by the Zeeman field, displays distinct behavior for opposite bias directions, and shows spatial dependence governed by the nature of the contributing modes. We also identify bound states at the junction for attractive barrier strengths, which enhance conductivity when their energies lie near the transport window. Our results reveal a mechanism for nonreciprocal transverse charge transport in Rashba systems without requiring in-plane magnetic fields or ferromagnetic contacts, and should be experimentally accessible in semiconductor heterostructures.

cond-mat.mes-hall↗

arXiv2026

Giant field-free transverse Josephson diode effect in altermagnets

We predict a field-free transverse Josephson diode effect in altermagnets (AMs) with Rashba spin--orbit coupling, achieving diode efficiencies exceeding $3000\%$ and unidirectional transverse supercurrents in four-terminal junctions. In this geometry, a longitudinal phase bias generates transverse supercurrents that exhibit nonreciprocity and a finite anomalous phase shift, while the longitudinal current itself displays a Josephson diode effect. Both responses are tunable via the Néel vector orientation. We further show that the effect remains robust against moderate disorder and imperfect interfaces. These results establish AMs as a promising platform for nonreciprocal superconducting transport, with clear routes toward experimental realization.

cond-mat.mes-hall↗

arXiv2026

Equilibrium spin currents in altermagnet junctions: Josephson-like and anomalous transport

Altermagnets (AMs) offer a compelling platform for exploring novel spin-dependent phenomena in materials with zero net macroscopic magnetization. In this work, we theoretically investigate the emergence of equilibrium spin currents (ESCs) in two-dimensional AM heterostructures using a tight-binding lattice model. We first study an AM-normal metal-AM (AM-NM-AM) junction and demonstrate that the $σ_y$-polarized ESC exhibits a characteristic Josephson-like behavior, fundamentally governed by the relative angle ($θ$) between the Néel vectors of the two AMs pointing in $xz$-plane. Crucially, we show that replacing the central normal metal with a $p$-wave magnet (PM) induces an anomalous ESC. Analogous to the anomalous Josephson effect, the breaking of spatial inversion symmetry by the PM allows a finite, dissipationless spin current to flow even when the Néel vectors are perfectly aligned ($θ=0$). We establish that this anomalous transport is driven by an asymmetry in the quantum phases accumulated by right- and left-moving electrons undergoing spin-flip reflections. Finally, we show that the critical ESC exhibits pronounced fluctuations as a function of band filling, which we attribute to mesoscopic quantum size effects, including transverse subband quantization and longitudinal Fabry-Pérot resonances. Our findings highlight the potential of altermagnet junctions for designing dissipationless, phase-tunable spintronic devices.

cond-mat.mes-hall↗

arXiv2026

Tunable Crossed Andreev Reflection in Bipolar Magnetic Semiconductors

Crossed Andreev reflection (CAR) is a nonlocal quantum transport phenomenon that arises at the interface between a superconductor and two spatially separated metals. In this process, an electron incident from one metal combines with another electron originating from the other metal to form a Cooper pair in the superconductor. As a consequence, a hole is emitted into the second metal, establishing a nonlocal electron-hole conversion process. In contrast to local Andreev reflection -- where electron-to-hole conversion occurs within the same region -- CAR intrinsically links two spatially separated carriers, giving rise to nonlocal correlations and quantum entanglement. In bipolar magnetic semiconductors (BMSs), the conduction and valence bands possess opposite spin polarizations. We propose to achieve tunable control of CAR by independently adjusting the chemical potentials of the two regions. By engineering the alignment of spin-polarized bands in the two BMS leads, CAR can be selectively enhanced or suppressed. This tunability enables precise manipulation of nonlocal transport, and correlated electron dynamics, offering promising prospects for spintronic and superconducting device applications.

cond-mat.mes-hall↗

arXiv2026

Transverse response from anisotropic Fermi surfaces

We demonstrate that an anisotropic and rotated Fermi surface can generate a finite transverse response in electron transport, even in the absence of a magnetic field or Berry curvature. Using a two-dimensional continuum model, we show that broken $k_y \to -k_y$ symmetry inherent to anistropic bandstructures leads to a nonzero transverse conductivity. We construct a lattice model with direction-dependent nearest- and next-nearest-neighbor hoppings that faithfully reproduces the continuum dispersion and allows controlled rotation of the Fermi contour. Employing a multiterminal geometry and the Büttiker-probe method, we compute the resulting transverse voltage and establish its direct correspondence with the continuum transverse response. The effect increases with the degree of anisotropy and vanishes at rotation angles where mirror symmetry is restored. Unlike the quantum Hall effect, the transverse response predicted here is not quantized but varies continuously with the band-structure parameters. Our results provide a symmetry-based route to engineer transverse signals in low-symmetry materials without magnetic fields or topological effects.

cond-mat.mes-hall↗

arXiv2026

Crystallographic Orientation-Dependent Magnetotransport in the Layered Antiferromagnet -- CrSBr

Among two-dimensional magnetic materials, CrSBr has attracted considerable attention owing to its coexistence of ferromagnetic and antiferromagnetic ordering, which depends sensitively on crystallographic orientation. An additional distinguishing feature of CrSBr is its highly anisotropic Fermi surface in momentum space. In this work, we present a comprehensive investigation of magnetoresistance by systematically orienting the bias current and the applied magnetic field along all three crystallographic axes. We demonstrate that the magnetoresistance serves as a direct probe of electronic anisotropy, exhibiting pronounced variations when the current is applied along different crystallographic directions under a magnetic field perpendicular to the sample plane. For in-plane magnetic fields, we observe conventional anisotropic magnetoresistance accompanied by hysteresis, indicative of ferromagnetic behavior. Overall, our study provides a complete picture of electronic transport in CrSBr as a function of bias current and magnetic field orientation with respect to crystallographic directions, thereby opening pathways for future experiments requiring high sensitivity of electrical resistance to magnetic field gradients.

cond-mat.mtrl-sci↗

arXiv2026

Geometry induced net spin polarization of $d$-wave altermagnets

Altermagnets exhibit spin-split electronic bandstructures despite having zero net magnetization, making them attractive for field-free spintronic applications. In this work, we show that a finite rectangular altermagnetic sample can acquire a net spin polarization purely due to its geometry. This effect arises from the interplay between the anisotropic, spin-resolved Fermi contours of an altermagnet, the discrete sampling of momentum space and unequal sample dimensions. By explicitly counting occupied states, we demonstrate that rectangular samples with $L_x \neq L_y$ host a finite spin polarization, which vanishes in the symmetric limit $L_x=L_y$ and in the thermodynamic limit. We further show that this geometry-induced spin polarization can be directly probed in transport measurements. In the tunneling regime, the charge and the spin conductances exhibit characteristic patterns as a function of sample dimensions, faithfully reflecting the underlying spin polarization. In addition, transport across ferromagnet--altermagnet--ferromagnet junctions reveals an asymmetric magnetoresistance with respect to reversal of the Zeeman field, providing an independent transport signature of the finite spin polarization. Our results establish geometry as an effective control parameter for spin polarization in altermagnets and suggest a viable route for exploiting finite-size effects in mesoscopic altermagnetic spintronic devices.

cond-mat.mes-hall↗

arXiv2026

Néel vector controlled charge and spin transport in altermagnetic junctions

Altermagnets (AMs) - magnetic materials that have spin-split bandstructure with zero net spin polarization can be classified as weak or strong depending upon the strength of altermagnetic term in the Hamiltonian. We theoretically investigate electron transport in junctions between the two AMs in strong and weak altermagnetic phases. The charge and spin conductivities are analyzed as functions of angle $θ$ between the Néel vectors of the two AMs. In the strong AM regime, the charge conductivity vanishes as $θ\to π$, while in the weak AM regime it remains finite. Introducing a normal metal (NM) between two AMs leads to Fabry-Pérot-type oscillations in charge conductivity which can be controlled by an applied gate voltage. In the strong regime, transport in AM-NM-AM junctions is dominated by up-spin electrons, whereas both spin channels contribute in the weak regime. These results highlight the potential of AM-based heterostructures for spintronic applications, such as spin filters, and quantum interference-based spintronic devices, where tunable spin-dependent transport and interference effects can be utilized in electronic devices without a need for externally applied magnetic field.

cond-mat.mes-hall↗

arXiv2025

Orientation dependent anomalous Hall and spin Hall currents at junctions of altermagnets with $p$-wave magnets

We study charge and spin transport across a junction between an altermagnet (AM) and a $p$-wave magnet (PM) using a continuum model with boundary conditions tailored to the spin-split band structures of the two materials. Remarkably, although neither AM nor PM is spin-polarized, we find that the junction supports finite spin currents both longitudinally and transversely. We compute the longitudinal and transverse charge and spin conductivities as functions of the crystallographic orientations and the relative angle between the Néel vectors of AM and PM. Our results reveal that transverse charge and spin conductivities can be finite even when the longitudinal charge conductivity vanishes. For suitable parameter choices and orientation angles, the transverse conductivities are more prominent than the longitudinal ones. The origin of these effects lies in the matching and mismatching of transverse momentum modes ($k_y$) across the junction combined with the spin-dependent band splitting in AM and PM. Furthermore, while the transverse charge conductivity may be zero for certain orientations, the transverse spin conductivity remains finite due to unequal contributions of opposite $k_y$ channels. These findings highlight AM-PM junctions as a promising platform for tunable generation and control of transverse charge and spin currents driven purely by crystallographic orientation and spin structure.

cond-mat.mes-hall↗

arXiv2025

Four-terminal Josephson junctions: diode effects, anomalous currents and transverse currents

We study a multi-terminal Josephson junction consisting of a central spin-orbit-coupled (SOC) region with an in-plane Zeeman field connected to four superconducting terminals. This setup allows for the simultaneous measurement of both longitudinal and transverse Josephson currents in response to a phase bias and provides a platform to probe the planar Hall effect in superconducting transport. We find that the system exhibits anomalous Josephson effect (AJE) and Josephson diode effect (JDE) when the symmetry between opposite momentum modes is broken in SOC region. Specifically, breaking the symmetry between $k_x$ and $-k_x$ results in JDE and AJE in the longitudinal Josephson current, while breaking the symmetry between $k_y$ and $-k_y$ leads to a finite transverse Josephson current that also exhibits JDE and AJE. Transverse Josephson diode effect coefficient attains values as large as $500\%$ for realistic set of parameters. Furthermore, for specific parameter choices, the current-phase relation in the transverse direction supports unidirectional transport, highlighting its potential for superconducting circuit applications. Our setup offers a new route to engineering nonreciprocal superconducting transport.

cond-mat.supr-con↗

arXiv2025

All-electrical scheme for valley polarization in graphene

We propose an all-electrical setup to generate valley polarization in graphene. A finite graphene sheet is connected to two normal metal electrodes each with two terminals along its zigzag edges, while the armchair edges remain free. When a bias is applied to one terminal and the others are grounded, valley polarization emerges due to transverse momentum matching between the graphene and the metal electrodes. Significant valley polarization is achieved when the Fermi wavevector in the metal exceeds half the separation between the $ K $ and $ K' $ valleys in graphene. We analyze how conductance and valley polarization depend on geometric and electronic parameters. While increasing the width enhances both conductance and polarization, increasing the length introduces Fabry--Pérot oscillations and suppresses valley polarization due to enhanced intervalley mixing. We also examine the effects of disorder: on-site disorder in graphene increases conductance near the Dirac point but reduces valley polarization. Finally, we study the impact of imperfect armchair edges and interface roughness, finding that moderate deviations from ideal conditions still yield substantial valley polarization. Our results demonstrate a viable route to electrically controlling valley degrees of freedom in graphene-based devices.

cond-mat.mes-hall↗

arXiv2025

Crossed Andreev reflection in collinear $p$-wave magnet/triplet superconductor junctions

Crossed Andreev reflection (CAR) is a fundamental quantum transport phenomenon that holds significant implications for spintronics and superconducting devices. However, its experimental detection and enhancement remain challenging. Recently, magnetic materials exhibiting $p$-wave magnetic ordering, distinct from conventional spin-orbit coupling, referred to as $p$-wave magnets, have attracted considerable interest. In this work, we propose a junction consisting of $p$-wave magnets and a triplet superconductor as a promising platform to enhance CAR. The setup features a triplet superconductor sandwiched between two collinear $p$-wave magnets rotated by $180^\circ$ relative to each other, allowing for precise control over transport processes. We demonstrate that CAR can dominate over electron tunneling (ET) within specific parameter regimes, such as the orientation angle of the $p$-wave magnets and their chemical potential. Enhanced CAR occurs when the constant energy contours of the two spins in the $p$-wave magnets are well-separated. Furthermore, the conductivities display Fabry-Pérot-type oscillations due to interference effects, with CAR diminishing as the length of the superconductor exceeds the decay length of the wavefunctions. These findings underscore the potential of collinear $p$-wave magnet-superconductor junctions as a robust platform for the experimental investigation and enhancement of CAR.

cond-mat.mes-hall↗

arXiv2024

Josephson diode effect in one-dimensional quantum wires connected to superconductors with mixed singlet-triplet pairing

The Josephson diode effect (JDE), characterized by asymmetric critical currents in a Josephson junction, has drawn considerable attention in the field of condensed matter physics. We investigate the conditions under which JDE can manifest in a one-dimensional Josephson junction composed of a spin-orbit-coupled quantum wire with an applied Zeeman field, connected between two superconductors. Our study reveals that while spin-orbit coupling (SOC) and a Zeeman field in the quantum wire are not sufficient to induce JDE when the superconductors are purely singlet, introduction of triplet pairing in the superconductors leads to the emergence of JDE. This finding highlights the potential of JDE as a probe for triplet superconductivity. We further demonstrate that even in absence of SOC in the quantum wire, JDE can arise when the directions of the triplet pairing and the Zeeman field are non-collinear, provided the superconductors exhibit mixed singlet-triplet pairing. Additionally, we identify specific conditions under which JDE is absent, namely, when the pairing is purely triplet and the directions of the SOC and the triplet pairing are perpendicular. Our findings indicate that JDE is always accompanied by anomalous Josephson effect. The diode effect coefficient is found to oscillate with variations in the chemical potential of the quantum wire, driven by Fabry-Pérot interference effects. Our results suggest that quantum wires connected across superconductors can serve as effective platforms for probing triplet superconductivity through the observation of JDE.

cond-mat.supr-con↗

arXiv2024

Persistent currents in mesoscopic spin-orbit coupled rings due to an applied Zeeman field

Persistent currents (PCs) in mesoscopic rings have been a subject of intense investigation since their proposal by Büttiker, Landauer, and Imry in 1983. In this paper, we explore the behavior of PC in spin-orbit coupled rings under the influence of a Zeeman field (without a need for a flux threading the ring), contrasting it with traditional PC observed in rings threaded by magnetic flux. Our study reveals that the emergence of PC in our setup crucially depends on nonzero values of spin-orbit coupling and the Zeeman field. Through theoretical analysis and numerical calculations, we uncover several intriguing phenomena. Specifically, in ballistic rings, we observe an inverse proportionality between PC and system size, with PC being zero at half filling for even numbers of sites. Additionally, the introduction of on-site disorder leads to the suppression of PC, with exponential decay observed for large disorder strengths and quadratic decay for smaller disorder strengths. Notably, disorder can enhance PC in individual samples, albeit with a configuration-averaged PC of zero. Furthermore, we find that the standard deviation of PC increases with disorder strength, reaching a maximum before decreasing to zero at high disorder strengths. We study the case of PC when the Zeeman field and the spin-orbit field are noncollinear. We also study persistent spin current which shows behavior similar to that of PC except that at half filling, it is not zero. Our findings shed light on the intricate interplay between spin-orbit coupling, Zeeman fields, and disorder in mesoscopic quantum systems, offering new avenues for theoretical exploration and experimental verification.

cond-mat.mes-hall↗