arXiv subjects

Pedro Schlottmann

Publications and source records attributed to Pedro Schlottmann.

18 recordsLinked to original sources

arXiv2026

Emergent Electronic Bond-Order Wave in a Quasi-One-Dimensional Chain

Collective order is notoriously difficult to stabilize in one dimension, where strong fluctuations suppress symmetry-breaking states. Here we report the emergence of an electronic bond-order wave (BOW) in the quasi-one-dimensional (1D) material Ba9Rh8O24, in which structural bonds become active electronic degrees of freedom that overcome 1D fluctuations to establish long-range order. Single-crystal X-ray diffraction uncovers a striking inversion of inequivalent Rh-Rh bonds across a transition TA = 180 K, where short and long bonds interchange their identities rather than undergoing conventional Peierls dimerization. This bond inversion coincides with a heat-capacity anomaly and a profound reorganization of the dielectric response with strong suppression of dielectric loss upon cooling. The BOW exhibits strongly nonlinear, frequency-dependent I-V characteristics, clockwise hysteresis, and nonvolatile memristive switching. These findings uncover an unprecedented transformation from a dynamic bond liquid to a rigid yet electrically reconfigurable BOW, establishing bond-centered electronic order as a new organizing principle for 1D quantum matter.

cond-mat.str-el↗

arXiv2026

Hidden Density-Wave Instability in the Trimer Ruthenate Ba$_4$Ru$_3$O$_{10}$

We report a hidden density-wave instability in the trimer-based ruthenate Ba4Ru3O10, previously regarded as a pure antiferromagnet with a phase transition at TA=100 K. This transition is manifested in lattice parameters, transport, thermodynamics, and magnetic susceptibility, yet remains remarkably insensitive to magnetic fields up to at least 14 T, indicating an electronically driven reconstruction. At much lower temperatures T*= 20 K, charge transport becomes strongly nonlinear, exhibiting distinct depinning thresholds, negative differential resistance, pronounced current- and frequency-dependence, and slow collective dynamics in the Hertz range. While each feature is characteristic of density-wave transport, their simultaneous occurrence in an antiferromagnetic oxide is unprecedented. All nonlinear signatures vanish upon only 3% Ir substitution, which preserves the crystal structure and insulating state, ruling out Joule heating or extrinsic artifacts. The wide separation between the electronic reconstruction at TA and the emergence of nonlinear dynamics at T* identifies Ba4Ru3O10 as a rare correlated system hosting a strongly pinned collective electronic state intertwined with antiferromagnetism.

cond-mat.str-el↗

arXiv2024

Interaction of Magnetic Fields with Spinons in a Fractionalized State

The 4d-electron trimer lattice exhibits either a quantum spin liquid (QSL) or a heavy-fermion strange metal (HFSM) phase, depending on Nb content. In the QSL state, itinerant spinons act as effective heat carriers, enhancing thermal conductivity. Strikingly, applying a magnetic field up to 14 T causes an abrupt increase in heat capacity by as much as 5000% below 150 mK, disrupting the linear temperature dependence characteristic of both phases. Meanwhile, AC magnetic susceptibility and electrical resistivity remain nearly unchanged, while thermal conductivity is suppressed by up to 40% below 4 K. These observations suggest that spinons, though charge-neutral, are highly sensitive to magnetic fields at low temperatures. We propose that the field induces Anderson localization of spinons, leading to emergent non-magnetic two-level systems that account for the rapid rise in heat capacity. These findings uncover a previously unexplored regime of spinon dynamics, governed by field-induced localization and distinct from conventional magnetic or transport signatures. Comments: To appear in npj Quantum Materials.

cond-mat.str-el↗

arXiv2024

Transition between heavy-fermion strange metal and quantum spin liquid in a 4d-electron trimer lattice

We present experimental evidence that a heavy Fermi surface consisting of itinerant, charge-neutral spinons underpins both heavy-fermion-strange-metal (without f electrons) and quantum-spin-liquid states in the 4d-electron trimer lattice, Ba4Nb1-xRu3+xO12 (|x| < 0.20). These two exotic states both exhibit an extraordinarily large entropy, a linear heat capacity extending into the milli-Kelvin regime, a linear thermal conductivity at low temperatures, and separation of charges and spins. Furthermore, the insulating spin liquid is a much better thermal conductor than the heavy-fermion-strange-metal that separately is observed to strongly violate the Wiedemann-Franz law. We propose that at the heart of this 4d system is a universal, heavy spinon Fermi surface that provides a unified framework for explaining the exotic phenomena observed throughout the entire series. The control of such exotic ground states provided by variable Nb concentration offers a new paradigm for studies of correlated quantum matter.

cond-mat.str-el↗

arXiv2024

Chirality-Induced Magnet-Free Spin Generation in a Semiconductor

Electrical generation and transduction of polarized electron spins in semiconductors are of central interest in spintronics and quantum information science. While spin generation in semiconductors has been frequently realized via electrical injection from a ferromagnet, there are significant advantages in nonmagnetic pathways of creating spin polarization. One such pathway exploits the interplay of electron spin with chirality in electronic structures or real space. Here, utilizing chirality-induced spin selectivity (CISS), we demonstrate efficient creation of spin accumulation in n-doped GaAs via electric current injection from a normal metal (Au) electrode through a self-assembled monolayer of chiral molecules (α-helix L-polyalanine, AHPA-L). The resulting spin polarization is detected as a Hanle effect in the n-GaAs, which is found to obey a distinct universal scaling with temperature and bias current consistent with chirality-induced spin accumulation. The experiment constitutes a definitive observation of CISS in a fully nonmagnetic device structure and demonstration of its ability to generate spin accumulation in a conventional semiconductor. The results thus place key constraints on the physical mechanism of CISS and present a new scheme for magnet-free semiconductor spintronics.

cond-mat.mes-hall↗

arXiv2023

Current-sensitive Hall effect in a chiral-orbital-current state

Chiral orbital currents (COC) underpin a novel colossal magnetoresistance (CMR) in ferrimagnetic Mn3Si2Te6 [1]. Here we report the Hall effect in the COC state which exhibits the following unprecedented features: (1) A sharp, current-sensitive peak in the magnetic field dependence of the Hall resistivity; (2) An unusually large Hall angle reaching up to 0.15 (comparable to the highest values yet reported); and (3) A current-sensitive scaling relation between the Hall conductivity sigma_xy and the longitudinal conductivity sigma_xx, namely, sigma_xy ~ sigma_xx^alpha with alpha ranging between 3 and 5, which is both sensitive to external current and exceptionally large compared to alpha < 2 typical of most solids. These anomalies point to a giant, current-sensitive Hall effect that is unique to the COC state. We argue that a magnetic field induced by the fully developed COC combines with the applied magnetic field to exert the greatly enhanced transverse force on charge carriers, which dictates the novel Hall responses. The COC Hall effect is unique, as it is generated and controlled via the interaction between intrinsic COC and applied external currents, which leads to novel transport phenomena of fundamental and technological significance and requires new physics for explanation.

cond-mat.str-el↗

arXiv2022

Interplay of Structural Chirality, Electron Spin and Topological Orbital in Chiral Molecular Spin Valves

Chirality has been a property of central importance in chemistry and biology for more than a century, and is now taking on increasing relevance in condensed matter physics. Recently, electrons were found to become spin polarized after transmitting through chiral molecules, crystals, and their hybrids. This phenomenon, called chirality-induced spin selectivity (CISS), presents broad application potentials and far-reaching fundamental implications involving intricate interplays among structural chirality, topological states, and electronic spin and orbitals. However, the microscopic picture of how chiral geometry influences electronic spin remains elusive. In this work, via a direct comparison of magnetoconductance (MC) measurements on magnetic semiconductor-based chiral molecular spin valves with normal metal electrodes of contrasting strengths of spin-orbit coupling (SOC), we unambiguously identified the origin of the SOC, a necessity for the CISS effect, given the negligible SOC in organic molecules. The experiments revealed that a heavy-metal electrode provides SOC to convert the orbital polarization induced by the chiral molecular structure to spin polarization. Our results evidence the essential role of SOC in the metal electrode for engendering the CISS spin valve effect. A tunneling model with a magnetochiral modulation of the potential barrier is shown to quantitatively account for the unusual transport behavior. This work hence produces critical new insights on the microscopic mechanism of CISS, and more broadly, reveals a fundamental relation between structure chirality, electron spin, and orbital.

cond-mat.mtrl-sci↗

arXiv2022

Mechanical control of physical properties in the van der Waals ferromagnet Cr2Ge2Te6 via application of electric current

Cr2Ge2Te6 is a van der Waals ferromagnet with a Curie temperature at 66 K. Here we report a swift change in the magnetic ground state upon application of small DC electric current, a giant yet anisotropic magnetoelectric effect, and a sharp, lattice-driven quantum switching manifested in the I-V characteristic of the bulk single-crystal Cr2Ge2Te6. At the heart of these observed phenomena is a newly uncovered, strongly anisotropic magnetoelastic coupling that enables strongly anisotropic responses of the lattice to application of electric current and/or magnetic field, thus the exotic phenomena in Cr2Ge2Te6. Such a rare mechanical tunability in the magnetic semiconductors promises tantalizing prospects for unique functional materials and devices.

cond-mat.mtrl-sci↗

arXiv2021

Impedance Spectroscopy of SmB$_6$ single crystals

We report results from an in--plane and out--of--plane impedance study on SmB$_6$ single crystals, performed at low temperatures and over a wide frequency range. A universal equivalent circuit describes the dielectric behavior of this system across the transition, from surface to bulk dominated electrical conduction between 2 and 10 K. We identify the resistive, capacitive, and inductive contributions to the impedance. The equivalent inductance, obtained from fits to experimental data, drops drastically as the bulk starts to control electrical conduction upon increasing temperature. SmB$_6$ single crystals also show current--controlled negative differential resistance at low temperatures, which is brought about by Joule heating. This feature, in addition to inductive and capacitive contributions to the impedance, can give rise to the self--sustained voltage oscillations observed below 5 K (Stern {\it et al.}, Phys. Rev. Lett. {\bf 116}, 166603 (2016)).

cond-mat.str-el↗

arXiv2021

The power of flexible lattice in Ca3Ru2O7: Exquisite control of the electrical transport via anisotropic magnetostriction

Ca3Ru2O7 is a correlated and spin-orbit-coupled system with an extraordinary anisotropy. It is both interesting and unique largely because this material exhibits conflicting phenomena that are often utterly inconsistent with traditional precedents, particularly, the quantum oscillations in the nonmetallic state and colossal magnetoresistivity achieved by avoiding a fully spin-polarized state. This work focuses on the relationship between the lattice and transport properties along each crystalline axis and reveals that application of magnetic field, H, along different crystalline axes readily stretches or shrinks the lattice in a uniaxial manner, resulting in distinct electronic states. Furthermore, application of modest pressure drastically amplifies the anisotropic magnetoelastic effect, leading to either an occurrence of a robust metallic state at H || hard axis or a reentrance of the nonmetallic state at H || easy axis. Ca3Ru2O7 presents a rare lattice-dependent magnetotransport mechanism, in which the extraordinary lattice flexibility enables an exquisite control of the electronic state via magnetically stretching or shrinking the crystalline axes, and the spin polarization plays an unconventional role unfavorable for maximizing conductivity. At the heart of the intriguing physics is the anisotropic magnetostriction that leads to exotic states.

cond-mat.str-el↗

arXiv2021

The ground state in a proximity to a possible Kitaev spin liquid: An undistorted honeycomb iridate NaxIrO3 (0.60 < x < 0.80)

We report results of our study of a newly synthesized honeycomb iridate NaxIrO3 (0.60 < x < 0.80). Single-crystal NaxIrO3 adopts a honeycomb lattice noticeably without distortions and stacking disorder inherently existent in its sister compound Na2IrO3. The oxidation state of the Ir ion is a mixed valence state resulting from a majority Ir5+(5d4) ion and a minority Ir6+(5d3) ion. NaxIrO3 is a Mott insulator likely with a predominant pseudospin = 1 state. It exhibits an effective moment of 1.1 Bohr Magneton/Ir and a Curie-Weiss temperature of -19 K but with no discernable long-range order above 1 K. The physical behavior below 1 K features two prominent anomalies at Th = 0.9 K and Tl = 0.12 K in both the heat capacity and AC magnetic susceptibility. Intermediate between Th and Tl lies a pronounced temperature linearity of the heat capacity with a large slope of 77 mJ/mole K2, a feature expected for highly correlated metals but not at all for insulators. These results along with comparison drawn with the honeycomb lattices Na2IrO3 and (Na0.2Li0.8)2IrO3 point to an exotic ground state in a proximity to a possible Kitaev spin liquid.

cond-mat.str-el↗

arXiv2020

Fortuitous partners of antiferromagnetic and Mott states in spin-orbit-coupled Sr2IrO4: A study of Sr2Ir1-xMxO4 (M=Fe or Co)

Sr2IrO4 is an archetypal spin-orbit-coupled Mott insulator with an antiferromagnetic state below 240 K. Here we report results of our study on single crystals of Sr2Ir1-xFexO4 (0<x<0.32) and Sr2Ir1-xCoxO4 (0<x<0.22). Fe doping retains the antiferromagnetic state but simultaneously precipitates an emergent metallic state whereas Co doping causes a rapid collapse of both the antiferromagnetic and Mott states, giving rise to a confined metallic state featuring a pronounced linearity of the basal-plane resistivity up to 700 K. The results indicate tetravalent Fe4+(3d4) ions in the intermediate spin state with S=1 and Co4+(3d5) ions in the high spin state with S=5/2 substituting for Ir4+(5d5) ions in Sr2IrO4, respectively. The effective magnetic moment closely tracks the Néel temperature as doping increases, suggesting that the spin state of the dopant predominately determines the magnetic properties in doped Sr2IrO4. Furthermore, all relevant properties including charge-carrier density (e.g., 1028/m3), Sommerfeld coefficient (e.g., 19 mJ/mole K2) and Wilson ratio (e.g., 2.6), consistently demonstrates a metallic state that is both robust and highly correlated in the two systems, arising from the percolation of bound states and the weakening of structural distortions. This study strongly suggests that the antiferromagnetic and Mott states merely coexist in a fortuitous manner in Sr2IrO4.

cond-mat.str-el↗

arXiv2020

Quest for New Quantum States via Field-Editing Technology

We report new quantum states in spin-orbit-coupled single crystals that are synthesized using a game-changing technology that "field-edits" crystal structures (borrowing from the phrase "genome editing") via application of magnetic field during crystal growth. This study is intended to fundamentally address a major challenge facing the research community today: A great deal of theoretical work predicting exotic states for strongly spin-orbit-coupled, correlated materials has thus far met very limited experimental confirmation. These conspicuous discrepancies are due chiefly to the extreme sensitivity of these materials to structural distortions. The results presented here demonstrate that the "field-edited" materials not only are much less distorted but also exhibit novel phenomena absent in their "non-edited" counterparts. The field-edited materials include an array of 4d and 5d transition metal oxides, and three representative materials presented here are Ba4Ir3O10, Ca2RuO4, and Sr2IrO4. This study provides an entirely new paradigm for discovery of new quantum states and materials otherwise unavailable.

cond-mat.str-el↗

arXiv2020

Bound fermion states in pinned vortices in the surface states of a superconducting topological insulator: The Majorana bound state

By analytically solving the Bogoliubov-de Gennes equations we study the fermion bound states at the center of the core of a vortex in a two-dimensional superconductor. We consider three kinds of 2D superconducting models: (a) a standard type II superconductor in the mixed state with low density of vortex lines, (b) a superconductor with strong spin-orbit coupling locking the spin parallel to the momentum and (c) a superconductor with strong spin-orbit coupling locking the spin perpendicular to the momentum. The 2D superconducting states are induced via proximity effect between an $s$-wave superconductor and the surface states of a strong topological insulator. In case (a) the energy gap for the excitations is of order $Δ_{\infty}^2/(2E_F)$, while for cases (b) and (c) a zero-energy Majorana state arises together with an equally spaced ($Δ^2_{\infty}/E_F$) sequence of fermion excitations. The spin-momentum locking is key to the formation of the Majorana state. We present analytical expressions for the energy spectrum and the wave functions.

cond-mat.supr-con↗

arXiv2019

Spin selectivity through chiral polyalanine monolayers on semiconductors

Electrical generation of polarized spins in nonmagnetic materials is of great interest for the underlying physics and device potential. One such mechanism is chirality-induced spin selectivity (CISS), with which structural chirality leads to different electric conductivities for electrons of opposite spins. The resulting effect of spin filtering has been reported for a number of chiral molecules. However, the microscopic mechanism and manifestation of CISS in practical device structures remain controversial; in particular, the Onsager relation is understood to preclude linear-response detection of CISS by a ferromagnet. Here, we report direct evidence of CISS in two-terminal devices of chiral molecules on the magnetic semiconductor (Ga,Mn)As: In vertical heterojunctions of (Ga,Mn)As/AHPA-L molecules/Au, we observed characteristic linear- and nonlinear-response magnetoconductance, which directly verifies spin filtering by the AHPA-L molecules and spin detection by the (Ga,Mn)As. The results constitute definitive signature of CISS-induced spin valve effect, a core spintronic functionality, in apparent violation of the Onsager reciprocity. The results present a promising route to semiconductor spintronics free of any magnetic material.

physics.app-ph↗

arXiv2017

The Challenge of Spin-Orbit-Tuned Ground States in Iridates

Effects of spin-orbit interactions in condensed matter are an important and rapidly evolving topic. Strong competition between spin-orbit, on-site Coulomb and crystalline electric field interactions in iridates drives exotic quantum states that are unique to this group of materials. In particular, the Jeff = 1/2 Mott state served as an early signal that the combined effect of strong spin-orbit and Coulomb interactions in iridates has unique, intriguing consequences. In this Key Issues Review, we survey some current experimental studies of iridates. In essence, these materials tend to defy conventional wisdom: absence of conventional correlations between magnetic and insulating states, avoidance of metallization at high pressures, S-shaped I-V characteristic, emergence of an odd-parity hidden order, etc. It is particularly intriguing that there exist conspicuous discrepancies between current experimental results and theoretical proposals that address superconducting, topological and quantum spin liquid phases. This class of materials, in which the lattice degrees of freedom play a critical role seldom seen in other materials, evidently presents some profound intellectual challenges that call for more investigations both experimentally and theoretically. Physical properties unique to these materials may help unlock a world of possibilities for functional materials and devices. We emphasize that, given the rapidly developing nature of this field, this Key Issues Review is by no means an exhaustive report of the current state of experimental studies of iridates.

cond-mat.str-el↗

arXiv2012

Kondo Physics in a Rare Earth Ion with Well Localized 4f Electrons

Dilute Nd in simple cubic LaB$_6$ shows electrical resistance and specific heat features at low temperature consistent with a Kondo scale of $T_K \lesssim$ 0.3 K. Nd has a well localized {\it 4f}$^{3}$ {\it J} = 9/2 Hund's Rule configuration which is not anticipated to be Kondo coupled to the conduction electrons in LaB$_6$. We conjecture that the unexpected Kondo effect arises via participation of {\it 4f} quadrupolar degrees of freedom of the Nd crystal field ground state quartet.

cond-mat.str-el↗

arXiv2011

Fermi gas with attractive potential and arbitrary spin in one-dimensional trap

A gas of ultracold $^6$Li atoms (effective spin 1/2) confined to an elongated trap with one-dimensional properties is a candidate to display three different phases: (i) fermions bound in Cooper-pair-like states, (ii) unbound spin-polarized particles, and (iii) a mixed phase which is believed to have some resemblance to the FFLO pairing. It is of great interest to extend these studies to fermionic atoms with higher spin, e.g., for neutral $^{40}$K, $^{43}$Ca, $^{87}$Sr or $^{173}$Yb atoms. Within the grand-canonical ensemble we investigated the $μ$ vs. $H$ phase diagram for $S=3/2$ ($μ$ is the chemical potential and $H$ the external magnetic field) for the ground state using the exact Bethe {\it ansatz} solution of the one-dimensional Fermi gas interacting with an attractive $δ$-function potential. There are four fundamental states: The particles can be either unpaired or clustered in bound states of two, three and four fermions. The rich phase diagram consists of these four states and various mixed phases in which combinations of the fundamental states coexist. Bound states of four fermions are not favorable in high magnetic fields, but always present if the field is low. Working within the grand-canonical ensemble has the following advantages: (1) A universal phase diagram is obtained by scaling with respect to the interaction strength and (2) possible scenarios for phase separation are explored within the local density approximation. The phase diagram for the superposition of a Zeeman and a quadrupolar splitting is also discussed.

cond-mat.quant-gas↗