arXiv subjects

Emi Minamitani

Publications and source records attributed to Emi Minamitani.

24 records · Page 2Linked to original sources

arXiv2018

Mechanically tunable spontaneous vertical charge redistribution in few-layer WTe2

Broken symmetry is the essence of exotic properties in condensed matters. Tungsten ditelluride, WTe$_2$, exceptionally takes a non-centrosymmetric crystal structure in the family of transition metal dichalcogenides, and exhibits novel properties$^{1-4}$, such as the nonsaturating magnetoresistance$^1$ and ferroelectric-like behavior$^4$. Herein, using the first-principles calculation, we show that unique layer stacking in WTe$_2$ generates surface dipoles with different strengths on the top and bottom surfaces in few-layer WTe$_2$. This leads to a layer-dependence for electron/hole carrier ratio and the carrier compensation responsible for the unusual magnetoresistance. The surface dipoles are tunable and switchable using the interlayer shear displacement. This could explain the ferroelectric-like behavior recently observed in atomically thin WTe$_2$ films$^4$. In addition, we reveal that exfoliation of the surface layer flips the out-of-plane spin textures. The presented results will aid in the deeper understanding, manipulation, and further exploration of the physical properties of WTe$_2$ and related atom-layered materials, for applications in electronics and spintronic devices.

cond-mat.mtrl-sci↗

arXiv2018

Phonon Angular Momentum Induced by Temperature Gradient

Phonon modes in crystals can have angular momenta in general. It nevertheless cancels in equilibrium when the time-reversal symmetry is preserved. In this paper we show that when a temperature gradient is applied and heat current flows in the crystal, the phonon distribution becomes off-equilibrium, and a finite angular momentum is generated by the heat current. This mechanism is analogous to the Edelstein effect in electronic systems. This effect requires crystals with sufficiently low crystallographic symmetries, such as polar or chiral crystal structures. Because of the positive charges of the nuclei, this phonon angular momentum induces magnetization. In addition, when the crystal can freely rotate, this generated phonon angular momentum is converted to a rigidbody rotation of the crystal, due to the conservation of the total angular momentum. Furthermore, in metallic crystals, the phonon angular momentum will be partially converted into spin angular momentum of electrons.

cond-mat.mes-hall↗

arXiv2017

Scanning tunneling spectroscopy of superconductivity on surfaces of LiTi2O4(111) thin films

Unique superconductivity at surfaces/interfaces, as exemplified by LaAlO3/SrTiO3 interfaces, and the high transition temperature in ultrathin FeSe films, have triggered intense debates on how superconductivity is affected in atomic and electronic reconstructions. The surface of superconducting cubic spinel oxide LiTi2O4 is another interesting system because its inherent surface electronic and atomic reconstructions add complexity to superconducting properties. Investigations of such surfaces are hampered by the lack of single crystals or high-quality thin films. Here, using low-temperature scanning tunneling microscopy, we report an unexpected small superconducting energy gap and a long coherence length on the surface of LiTi2O4 (111) epitaxial thin films. Furthermore, we find that a pseudogap opening at the Fermi energy modifies the surface superconductivity. Our results open an avenue, exploring anomalous superconductivity on the surface of cubic transition-metal oxides where the electronic states are spontaneously modulated with involving rich many-body interactions.

cond-mat.supr-con↗

arXiv2016

Two-dimensional atomic layer-molecule hybrid superconductors with controllable exchange coupling

The coexistence and competition of superconductivity and magnetism can lead to a variety of rich physics and technological applications. Recent discovery of atomic-layer superconductors and self-assembly of magnetic molecules on solid surfaces should allow one to create a new two-dimensional (2D) hybrid superconducting system, but its possibility has never been fully investigated so far. Here we report the fabrication of highly ordered 2D hybrid superconductors based on indium atomic layers on silicon surfaces and magnetic metal-phthalocyanines (MPc) and clarify their detailed structural, superconducting and magnetic properties. Our primary findings include a substantial controllability of the superconducting transition temperatures (Tc) through substitution of central metal ions (M = Cu, Fe, Mn) of the molecules. This is attributed to charge transfers between the magnetic molecules and the superconducting layers and to different degrees of exchange coupling between them, which originates from anisotropic distributions of the relevant d-orbitals. The present study opens a route for designing and creating exotic 2D superconductors with an atomic-scale precision.

cond-mat.supr-con↗

arXiv2015

Electronic and magnetic influences of a stacking fault in cobalt nanoscale islands on the Ag(111) surface

Utilizing spin-polarized scanning tunneling microscopy and spectroscopy, we found coexistence of perpendicularly and in-plane magnetized cobalt nanoscale islands on the Ag(111) surface, and the relationship between the moire corrugation amplitude and the magnetization direction of the islands; the islands with the stronger moire corrugation show the perpendicular magnetization, and the ones with the weaker moire corrugation do the in-plane. Density functional theory calculations reproduce the relationship and explain the differences between the two types of the islands with an fcc stacking fault in the intrinsic hcp stacking of cobalt.

cond-mat.mes-hall↗

arXiv2009

Scanning tunneling spectroscopic evidence of crossover transition in the two-impurity Kondo problem

We calculate the differential conductance (dI/dV) corresponding to scanning tunneling spectroscopy (STS) measurements for two magnetic atoms adsorbed on a metal surface with the aid of the numerical renormalization group (NRG) technique. We find that the peak structure of the dI/dV spectra near the Fermi level changes gradually as a function of the adatom separation and the coupling between the adatoms and the metal surface conduction band. When the coupling becomes small, the peak disappears and, instead, a dip structure appears near the Fermi level. This dip structure is the manifestation of the strong antiferromagnetic correlation between the localized spins. The gradual change of the dI/dV structure from a peak structure to a dip structure originates from the crossover transition in the two impurity Kondo problem.

cond-mat.mtrl-sci↗