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Igor I. Mazin

Publications and source records attributed to Igor I. Mazin.

At least 55 records · Page 3Linked to original sources
arXiv2023

Ising superconductivity: a first-principles perspective

The recent discovery of Ising superconductivity has garnered a lot of interest due in part to the resilience of these superconductors to large in-plane magnetic fields. In this Perspective we explain the basic concepts that define the behavior of Ising superconductors, provide an overview of the electronic structure and magnetic properties with a focus on NbSe$_2$, summarize key experimental observations that have been made in this class of superconductors, highlight the role that defects and proximity-induced effects at interfaces have on Ising superconductivity and finally discuss the prospects for observing Ising superconductivity in bulk materials.

cond-mat.supr-con↗
arXiv2023

Protection of Ising spin-orbit coupling in bulk misfit superconductors

Low-dimensional materials have remarkable properties that are distinct from their bulk counterparts. A paradigmatic example is Ising superconductivity that occurs in monolayer materials such as NbSe2 which show a strong violation of the Pauli limit. In monolayers, this occurs due to a combination of broken inversion symmetry and spin-orbit coupling that locks the spins of the electrons out-of-plane. Bulk NbSe2 is centrosymmetric and is therefore not an Ising superconductor. We show that bulk misfit compound superconductors, (LaSe)1.14(NbSe2) and (LaSe)1.14(NbSe2)2, comprised of monolayers and bilayers of NbSe2, exhibit unexpected Ising protection with a Pauli-limit violation comparable to monolayer NbSe2, despite formally having inversion symmetry. We study these misfit compounds using complementary experimental methods in combination with first-principles calculations. We propose theoretical mechanisms of how the Ising protection can survive in bulk materials. We show how some of these mechanisms operate in these bulk compounds due to a concerted effect of charge-transfer, defects, reduction of interlayer hopping, and stacking. This highlights how Ising superconductivity can, unexpectedly, arise in bulk materials, and possibly enable the design of bulk superconductors that are resilient to magnetic fields.

cond-mat.supr-con↗
arXiv2023

Heterogeneous Ta-dichalcogenide bilayer: heavy fermions or doped Mott physics?

Controlling and understanding electron correlations in quantum matter is one of the most challenging tasks in materials engineering. In the past years a plethora of new puzzling correlated states have been found by carefully stacking and twisting two-dimensional van der Waals materials of different kind. Unique to these stacked structures is the emergence of correlated phases not foreseeable from the single layers alone. In Ta-dichalcogenide heterostructures made of a good metallic 1H- and a Mott-insulating 1T-layer, recent reports have evidenced a cross-breed itinerant and localized nature of the electronic excitations, similar to what is typically found in heavy fermion systems. Here, we put forward a new interpretation based on first-principles calculations which indicates a sizeable charge transfer of electrons (0.4-0.6 e) from 1T to 1H layers at an elevated interlayer distance. We accurately quantify the strength of the interlayer hybridization which allows us to unambiguously determine that the system is much closer to a doped Mott insulator than to a heavy fermion scenario. Ta-based heterolayers provide therefore a new ground for quantum-materials engineering in the regime of heavily doped Mott insulators hybridized with metallic states at a van der Waals distance.

cond-mat.str-el↗
arXiv2023

Thermodynamic stability of Li-B-C compounds from first principles

Prediction of high-$T_{\rm{c}}$ superconductivity in hole-doped Li$_x$BC two decades ago has brought about an extensive effort to synthesize new materials with honeycomb B-C layers, but the thermodynamic stability of Li-B-C compounds remains largely unexplored. In this study, we use density functional theory to characterize well-established and recently reported Li-B-C phases. Our calculation of the Li chemical potential in Li$_x$BC helps estimate the ($T$,$P$) conditions required for delithiation of the LiBC parent material, while examination of B-C phases helps rationalize the observation of metastable BC$_3$ polymorphs with honeycomb and diamond-like morphologies. At the same time, we demonstrate that recently reported BC$_3$, LiBC$_3$, and Li$_2$B$_2$C phases with new crystal structures are both dynamically and thermodynamically unstable. With a combination of evolutionary optimization and rational design, we identify considerably more natural and favorable Li$_2$B$_2$C configurations that, nevertheless, remain above the thermodynamic stability threshold.

cond-mat.mtrl-sci↗
arXiv2022

A Punch line: altermagnetism

This is the first version of the editorial foreword to the Perspective review "Research Landscape of Altermagnetism" by L. Šmejkal, et al, published in Phys. Rev. X 12, 040501 (2022). Due to various editorial constraints the publish version (DOI:10.1103/PhysRevX.12.040002) deviates substantially from the initial text. This posting intends to make this original version available for perusal of potential readers.

cond-mat.mtrl-sci↗
arXiv2022

CrRhAs: a member of a large family of metallic kagome antiferromagnets

Kagome lattice materials are an important platform for highly frustrated magnetism as well as for a plethora of phenomena resulting from flat bands, Dirac cones and van Hove singularities in their electronic structures. We study the little known metallic magnet CrRhAs, which belongs to a vast family of materials that include $3d$, $4f$ and $5f$ magnetic elements, as well as numerous nonmagnetic metals and insulators. Using noncollinear spin density functional calculations (mostly spin spirals), we extract a model magnetic Hamiltonian for CrRhAs. While it is dominated by an antiferromagnetic second nearest neighbor coupling in the kagome plane, the metallic nature of the compound leads to numerous nonzero longer range couplings and to important ring exchange terms. We analyze this Hamiltonian and find unusual ground states which are dominated by nearly isolated antiferromagnetic triangles that adopt 120$^\circ$ order either with positive or with negative vector chirality. We discuss the connection to the few known experimental facts about CrRhAs. Finally, we give a brief survey of other interesting magnetic members of this family of kagome compounds.

cond-mat.str-el↗
arXiv2022

Hybrid s-wave superconductivity in CrB$_2$

In a metal with multiple Fermi pockets, the formation of s-wave superconductivity can be conventional due to electron-phonon coupling or unconventional due to spin fluctuations. We analyze the hexagonal diboride CrB$_2$, which is an itinerant antiferromagnet at ambient conditions and turns superconducting upon increasing pressure. While the high pressure behavior of T$_c$ suggests conventional s-wave pairing, we find that spin fluctuations promoting unconventional s-wave pairing become important in the vicinity of the antiferromagnetic dome. As the symmetry class of the s-wave state is independent of its underlying mechanism, we argue that CrB$_2$ is a realization of a hybrid s-wave superconductor where unconventional and conventional s-wave mechanisms team up to form a joint superconducting dome.

cond-mat.supr-con↗
arXiv2022

CoTe2: A quantum critical Dirac metal with strong spin fluctuations

Quantum critical points separating weak ferromagnetic and paramagnetic phases trigger many novel phenomena. Dynamical spin fluctuations not only suppress the long-range order, but can also lead to unusual transport and even superconductivity. Combining quantum criticality with topological electronic properties presents a rare and unique opportunity. Here, by means of ab initio calculations and magnetic, thermal, and transport measurements, we show that the orthorhombic CoTe$_2$ is close to ferromagnetism, which appears suppressed by spin fluctuations. Calculations and transport measurements reveal nodal Dirac lines, making it a rare combination of proximity to quantum criticality and Dirac topology.

cond-mat.str-el↗
arXiv2022

$Ab~initio$ study of Li-Mg-B superconductors

LiB, a predicted layered compound analogous to the MgB$_2$ superconductor, has been recently synthesized via cold compression and quenched to ambient pressure, yet its superconducting properties have not been measured. According to prior isotropic superconductivity calculations, the critical temperature ($T_{\rm{c}}$) was expected to be only 10$-$15 K. Using the anisotropic Migdal-Eliashberg formalism, we show that the $T_{\rm{c}}$ may actually exceed 32 K. Our analysis of the contribution from different electronic states helps explain the detrimental effect of pressure and doping on the compound's superconducting properties. In the search for related superconductors, we screened Li-Mg-B binary and ternary layered materials and found metastable phases with $T_{\rm{c}}$ close to or even 10$-$20% above the record 39 K value in MgB$_2$. Our reexamination of the Li-B binary phase stability reveals a possible route to synthesize the LiB superconductor at lower pressures readily achievable in multianvil cells.

cond-mat.supr-con↗
arXiv2022

Electronic and magnetic properties of the RuX$_3$ (X=Cl, Br, I) family: Two siblings -- and a cousin?

Motivated by recent reports of metallic behavior in the recently synthesized RuI$_3$, in contrast to the Mott-insulating nature of the actively discussed $α$-RuCl$_3$, as well as RuBr$_3$, we present a detailed comparative analysis of the electronic and magnetic properties of this family of trihalides. Using a combination of first-principles calculations and effective-model considerations, we conclude that RuI$_3$, similarly to the other two members, is most probably on the verge of a Mott insulator, but with much smaller magnetic moments and a strong magnetic frustration. We predict the ideal pristine crystal of RuI$_3$ to have a nearly vanishing conventional nearest-neighbor Heisenberg interaction and to be a quantum spin liquid candidate of possibly different kind than the Kitaev spin liquid. In order to understand the apparent contradiction to the reported resistivity $ρ$, we analyze the experimental evidence for all three compounds and propose a scenario for the observed metallicity in existing samples of RuI$_3$. Furthermore, for the Mott insulator RuBr$_3$ we obtain a magnetic Hamiltonian of a similar form to that in the much discussed $α$-RuCl$_3$ and show that this Hamiltonian is in agreement with experimental evidence in RuBr$_3$.

cond-mat.str-el↗
arXiv2022

Electron-phonon coupling strength from ab initio frozen-phonon approach

We propose a fast method for high-throughput screening of potential superconducting materials. The method is based on calculating metallic screening of zone-center phonon modes, which provides an accurate estimate for the electron-phonon coupling strength. This method is complementary to the recently proposed Rigid Muffin Tin (RMT) method, which amounts to integrating the electron-phonon coupling over the entire Brillouin zone (as opposed to the zone center), but in a relatively inferior approximation. We illustrate the use of this method by applying it to MgB$_\text{2}$, where the high-temperature superconductivity is known to be driven largely by the zone-center modes, and compare it to a sister compound AlB$_\text{2}$. We further illustrate the usage of this descriptor by screening a large number of binary hydrides, for which accurate first-principle calculations of electron-phonon coupling have been recently published. Together with the RMT descriptor, this method opens a way to perform initial high-throughput screening in search of conventional superconductors via machine learning or data mining.

cond-mat.supr-con↗
arXiv2022

Magnetic dilution effect and topological phase transitions in (Mn$_{1-x}$Pb$_x$)Bi$_2$Te$_4$

As the first intrinsic antiferromagnetic (AFM) topological insulator (TI), MnBi$_2$Te$_4$ has provided a material platform to realize various emergent phenomena arising from the interplay of magnetism and band topology. Here by investigating (Mn$_{1-x}$Pb$_x$)Bi$_2$Te$_4$ $(0\leq x \leq 0.82)$ single crystals via the x-ray, electrical transport, magnetometry and neutron measurements, chemical analysis, external pressure, and first-principles calculations, we reveal the magnetic dilution effect on the magnetism and band topology in MnBi$_2$Te$_4$. With increasing $x$, both lattice parameters $a$ and $c$ expand linearly by around 2\%. All samples undergo the paramagnetic to A-type antiferromagnetic transition with the N$\acute{e}$el temperature decreasing lineally from 24 K at $x=0$ to 2 K at $x=0.82$. Our neutron data refinement of the $x=0.37$ sample indicates that the ordered moment is 4.3(1)$μ_B$/Mn at 4.85 K and the amount of the Mn$_{\rm{Bi}}$ antisites is negligible within the error bars. Isothermal magnetization data reveal a slight decrease of the interlayer plane-plane antiferromagnetic exchange interaction and a monotonic decrease of the magnetic anisotropy, due to diluting magnetic ions and enlarging the unit cell. For $x=0.37$, the application of external pressures enhances the interlayer antiferromagnetic coupling, boosting the N$\acute{e}$el temperature at a rate of 1.4 K/GPa and the saturation field at a rate of 1.8 T/GPa. Furthermore, our first-principles calculations reveal that the band inversion in the two end materials, MnBi$_2$Te$_4$ and PbBi$_2$Te$_4$, occurs at the $Γ$ and $Z$ point, respectively, while two gapless points appear at $x = $ 0.44 and $x = $ 0.66, suggesting possible topological phase transitions with doping.

cond-mat.mtrl-sci↗
arXiv2022

Inverse Occam's razor

Scientists have long preferred the simplest possible explanation of their data. More re-cently, a worrying trend to favor complex interpretations has taken hold because they are perceived as more impactful.

physics.pop-ph↗
arXiv2022

Unconventional pressure-driven metamagnetic transitions in topological van der Waals magnets

Activating metamagnetic transitions between ordered states in van der Waals magnets and devices bring great opportunities in spintronics. We show that external pressure, which enhances the interlayer hopping without introducing chemical disorders, triggers multiple metamagnetic transitions upon cooling in the topological van der Waals magnets Mn(Bi$_{1-x}$Sb$_x$)$_4$Te$_7$, where the antiferromagnetic interlayer superexchange coupling competes with the ferromagnetic interlayer coupling mediated by the antisite Mn spins. The temperature-pressure phase diagrams reveal that while the ordering temperature from the paramagnetic to ordered states is almost pressure-independent, the metamagnetic transitions show non-trivial pressure and temperature dependence, even re-entrance. For these highly anisotropic magnets, we attribute the former to the ordering temperature being only weakly dependent on the intralayer parameters, the latter to the parametrically different pressure and temperature dependence of the two interlayer couplings. Our independent probing of these disparate magnetic interactions paves an avenue for efficient magnetic manipulations in van der Waals magnets.

cond-mat.str-el↗
arXiv2021

Phase diagram of a distorted kagome antiferromagnet and application to Y-kapellasite

We investigate the magnetism of a previously unexplored distorted spin-1/2 kagome model consisting of three symmetry-inequivalent nearest-neighbor antiferromagnetic Heisenberg couplings Jhexagon, J and J', and uncover a rich ground state phase diagram even at the classical level. Using analytical arguments and numerical techniques we identify a collinear Q = 0 magnetic phase, two unusual non-collinear coplanar Q = (1/3,1/3) phases and a classical spin liquid phase with a degenerate manifold of non-coplanar ground states, resembling the jammed spin liquid phase found in the context of a bond-disordered kagome antiferromagnet. We further show with density functional theory calculations that the recently synthesized Y-kapellasite Y3Cu9(OH)19Cl8 is a realization of this model and predict its ground state to lie in the region of Q = (1/3,1/3) order, which remains stable even after inclusion of quantum fluctuation effects within variational Monte Carlo and pseudofermion functional renormalization group. The presented model opens a new direction in the study of kagome antiferromagnets.

cond-mat.str-el↗
arXiv2021

Tuning the magnetism and band topology through antisite defects in Sb doped MnBi4Te7

The fine control of magnetism and electronic structure is crucial since the interplay between magnetism and band topology can lead to various novel magnetic topological states including axion insulators, magnetic Weyl semimetals and Chern insulators etc. Through crystal growth, transport, thermodynamic, neutron diffraction measurements, we show that with Sb-doping, the newly-discovered intrinsic antiferromagnetic topological insulator MnBi4Te7 evolves from antiferro-magnetic to ferromagnetic and then ferrimagnetic. We attribute this to the formation of Mn(Bi,Sb) antisites upon doping, which result in additional Mn sublattices that modify the delicate interlayer magnetic interactions and cause the dominant Mn sublattice to go from antiferromagnetic to ferro-magnetic. We further investigate the effect of antisites on the band topology using the first-principles calculations. Without considering antisites, the series evolves from antiferromagnetic topological insulator (x = 0) to ferromagnetic axion insulators. In the exaggerated case of 16.7% of periodic antisites, the band topology is modified and type-I magnetic Weyl semimetal phase can be realized at intermediate dopings. Therefore, this doping series provides a fruitful platform with continuously tunable magnetism and topology for investigating emergent phenomena, including quantum anomalous Hall effect, Fermi arc states, etc.

cond-mat.str-el↗
arXiv2021

Spin Spiral and Topological Hall Effect in a Metamagnet Fe$_{3}$Ga$_{4}$

A new mechanism for Topological Hall Effect (THE) was recently proposed for the spiral magnet YMn$_{6}$Sn$_{6},$ which requires transverse conical spiral (TCS) magnetism, induced by external magnetic field, combined with thermally excite helical spiral magnons. In principle, this mechanism should be applicable to other itinerant spiral magnets as well. In this paper, we show that another metamagnetic compound, Fe$_{3}$Ga$_{4}$, where THE was observed experimentally before, in one of its phases satisfies this condition, and the proposed theory of thermal-fluctuation driven THE is quantitatively consistent with the experiment. This finding suggests that this mechanism is indeed rather universal, and the effect may have been observed in other compounds before, but overlooked.

cond-mat.mtrl-sci↗