arXiv subjects

Hu Miao

Publications and source records attributed to Hu Miao.

At least 37 records · Page 2Linked to original sources

arXiv2023

Paramagnon dispersion and damping in doped Na$_{x}$Ca$_{2-x}$CuO$_2$Cl$_2$

Using Resonant Inelastic X-ray Scattering, we measure the paramagnon dispersion and damping of undoped, antiferromagnetic Ca$_2$CuO$_2$Cl$_2$ as well as doped, superconducting Na$_{x}$Ca$_{2-x}$CuO$_2$Cl$_2$. Our estimation of the spin-exchange parameter and width of the paramagnon peak at the zone boundary $X=(0.5,0)$ confirms that no simple relation can be drawn between these parameters and the critical temperature $T_\mathrm{c}$. Consistently with other cuprate compounds, we show that upon doping there is a slight softening at $(0.25,0)$, but not at the zone boundary $X$. In combination with these measurements we perform calculations of the dynamical spin structure factor of the one-band Hubbard model using cluster dynamical mean-field theory. The calculations are in excellent agreement with the experiment in the undoped case, both in terms of energy position and width. While the increase in width is also captured upon doping, the dynamical spin structure factor shows a sizable softening at $X$, which provides insightful information on the length-scale of the spin fluctuations in doped cuprates.

cond-mat.supr-con↗

arXiv2023

The sample-dependent and sample-independent thermal transport properties of $α$-RuCl$_3$

We investigated the thermal transport properties of two $α$-RuCl$_3$ crystals with different degrees of stacking disorder to understand the origin of the previously reported oscillatory feature in the field dependence of thermal conductivity. Crystal I shows only one magnetic order around 13\,K, which is near the highest T$_N$ for $α$-RuCl$_3$ with stacking faults. Crystal II has less stacking disorder, with a dominant heat capacity at 7.6\,K along with weak anomalies at 10\,K and 13\,K. In the temperature and field dependence of thermal conductivity, no obvious anomaly was observed to be associated with the magnetic order around 13\,K for either crystal or around 10\,K for crystal II. Crystal II, with less disorder, showed clear oscillations in the field dependence of thermal conductivity, while crystal I, with more disorder, did not. For crystal I, an L-shaped region in the temperature-field space was observed where thermal Hall conductivity $κ_{xy}$/T is within $\pm$20\% of the half quantized thermal Hall conductivity $κ_{HQ}$/T. While for crystal II, $κ_{xy}$/T reaches $κ_{HQ}$/T only in the high field and high temperature regime with no indication of a plateau at $κ_{HQ}$/T. Our thermal conductivity data suggest the oscillatory features are inherent to the zig-zag ordered phase with T$_N$ near 7\,K. Our planar thermal Hall effect measurements highlight the sensitivity of this phenomena to stacking disorder. Overall, our results highlight the importance of understanding and controlling crystallographic disorder for obtaining and interpreting intrinsic thermal transport properties in $α$-RuCl$_3$.

cond-mat.mtrl-sci↗

arXiv2023

Revealing intrinsic vortex-core states in Fe-based superconductors through machine-learning-driven discovery

Electronic states within superconducting vortices hold crucial information about paring mechanisms and topology. While scanning tunneling microscopy/spectroscopy(STM/S) can image the vortices, it is difficult to isolate the intrinsic electronic states from extrinsic effects like subsurface defects and disorders. We combine STM/S with unsupervised machine learning to develop a method for screening out the vortices pinned by embedded disorder in Fe-based superconductors. The approach provides an unbiased way to reveal intrinsic vortex-core states and may address puzzles on Majorana zero modes.

cond-mat.supr-con↗

arXiv2022

Imaging real-space flat band localization in kagome magnet FeSn

Kagome lattices host flat bands due to their frustrated lattice geometry, which leads to destructive quantum interference of electron wave functions. Here, we report imaging of the kagome flat band localization in real-space using scanning tunneling microscopy. We identify both the Fe3Sn kagome lattice layer and the Sn2 honeycomb layer with atomic resolution in kagome antiferromagnet FeSn. On the Fe3Sn lattice, at the flat band energy determined by the angle resolved photoemission spectroscopy, tunneling spectroscopy detects an unusual state localized uniquely at the Fe kagome lattice network. We further show that the vectorial in-plane magnetic field manipulates the spatial anisotropy of the localization state within each kagome unit cell. Our results are consistent with the real-space flat band localization in the magnetic kagome lattice. We further discuss the magnetic tuning of flat band localization under the spin-orbit coupled magnetic kagome lattice model.

cond-mat.str-el↗

arXiv2022

Monolayer superconductivity and tunable topological electronic structure at the Fe(Te,Se)/Bi2Te3 interface

The interface between two-dimensional topological Dirac states and an s-wave superconductor is expected to support Majorana bound states that can be used for quantum computing applications. Realizing these novel states of matter and their applications requires control over superconductivity and spin-orbit coupling to achieve spin-momentum locked topological surface states which are simultaneously superconducting. While signatures of Majorana bound states have been observed in the magnetic vortex cores of bulk FeTe0.55Se0.45, inhomogeneity and disorder from doping makes these signatures unclear and inconsistent between vortices. Here we report superconductivity in monolayer FeTe1-ySey (Fe(Te,Se)) grown on Bi2Te3 by molecular beam epitaxy. Spin and angle resolved photoemission spectroscopy directly resolve the interfacial spin and electronic structure of Fe(Te,Se)/Bi2Te3 heterostructures. We find that for y = 0.25 the Fe(Te,Se) electronic structure overlaps with the topological Bi2Te3 interfacial states which disrupts the desired spin-momentum locking. In contrast, for y = 0.1 a smaller Fe(Te,Se) Fermi surface allows for clear spin-momentum locking observed in the topological states. Hence, we demonstrate the Fe(Te,Se)/Bi2Te3 system is a highly tunable platform for realizing Majorana bound states where reduced doping can improve characteristics important for Majorana interrogation and potential applications.

cond-mat.supr-con↗

arXiv2022

On the Role of Defects in the Electronic Structure of MnBi$_{2-x}$Sb$_x$Te$_4$

Elemental substitution is a proven method of Fermi level tuning in topological insulators, which is needed for device applications. Through static and time resolved photoemission, we show that in MnBi$_2$Te$_4$, elemental substitution of Bi with Sb indeed tunes the Fermi level towards the bulk band gap, making the material charge neutral at 35\% Sb concentration. For the first time, we are able to directly probe the excited state band structure at this doping level, and their dynamics, which show that the decay channels at the Fermi level are severely restricted. However, elemental substitution widens the surface state gap, which we attribute to the increase in antisite defects resulting from Sb substitution. This hypothesis is supported by DFT calculations that include defects, which show a sensitivity of the topological surface state to their inclusion. Our results emphasize the need for defect control if MnBi$_{2-x}$Sb$_x$Te$_4$ is to be used for device applications.

cond-mat.mtrl-sci↗

arXiv2022

Bulk charge density wave and electron-phonon coupling in superconducting copper oxychlorides

Bulk charge density waves are now reported in nearly all high-temperature superconducting cuprates, with the noticeable exception of one particular family: the copper oxychlorides. Here, we used resonant inelastic X-ray scattering to reveal a bulk charge density waves in these materials. Combining resonant inelastic X-ray scattering with non-resonant inelastic X-ray scattering, we investigate the interplay between the lattice excitations and the charge density wave, and evidence the phonon anomalies of the Cu-O bond-stretching mode at the charge density wave wave-vector. We propose that such electron-phonon anomalies occur in the presence of dispersive charge excitations emanating from the charge density wave and interacting with the Cu-O bond-stretching phonon. Our results pave the way for future studies, combining both bulk and surface probes, to investigate the static and dynamical properties of the charge density wave in the copper oxychloride family.

cond-mat.supr-con↗

arXiv2022

Topological Electronic Structure Evolution with Symmetry Breaking Spin Reorientation in (Fe$_{1-x}$Co$_{x}$)Sn

Topological materials hosting kagome lattices have drawn considerable attention due to the interplay between topology, magnetism, and electronic correlations. The (Fe$_{1-x}$Co$_x$)Sn system not only hosts a kagome lattice but has a tunable symmetry breaking magnetic moment with temperature and doping. In this study, angle resolved photoemission spectroscopy and first principles calculations are used to investigate the interplay between the topological electronic structure and varying magnetic moment from the planar to axial antiferromagnetic phases. A theoretically predicted gap at the Dirac point is revealed in the low temperature axial phase but no gap opening is observed across a temperature dependent magnetic phase transition. However, topological surface bands are observed to shift in energy as the surface magnetic moment is reduced or becomes disordered over time during experimental measurements. The shifting surface bands may preclude the determination of a temperature dependent bulk gap but highlights the intricate connections between magnetism and topology with a surface/bulk dichotomy that can affect material properties and their interrogation.

cond-mat.str-el↗

arXiv2022

Phonon Chirality Induced by Vibronic-Orbital Coupling

The notion that phonons can carry pseudo-angular momentum has become popular in the last decade, with recent research efforts highlighting phonon chirality, Berry curvature of phonon band structure, and the phonon Hall effect. When a phonon is resonantly coupled to a crystal electric field excitation, a so-called vibronic bound state forms. Here, we observe angular momentum transfer of $δ$Jz = $\pm$1$\hbar$ between phonons and an orbital state in a vibronic bound state of a candidate quantum spin liquid. This observation has profound implications for the engineering of phonon band structure topology through chiral quasiparticle interactions.

cond-mat.mes-hall↗

arXiv2022

Semi-Dirac and Weyl Fermions in Transition Metal Oxides

We show that a class of compounds with $I$4/$mcm$ crystalline symmetry hosts three-dimensional semi-Dirac fermions. Unlike the known two-dimensional semi-Dirac points, the degeneracy of these three-dimensional semi-Dirac points is not lifted by spin-orbit coupling due to the protection by a nonsymmorphic symmetry -- screw rotation in the $a-b$ plane and a translation along the $c$ axis. This crystalline symmetry is found in tetragonal perovskite oxides, realizable in thin films by epitaxial strain that results in a$^0$a$^0$c$^-$-type octahedral rotation. Interestingly, with broken time-reversal symmetry, two pairs of Weyl points emerge from the semi-Dirac points within the Brillouin zone, and an additional lattice distortion leads to enhanced intrinsic anomalous Hall effect. The ability to tune the Berry phase by epitaxial strain can be useful in novel oxide-based electronic devices.

cond-mat.str-el↗

arXiv2021

Self-regulated growth of candidate topological superconducting parkerite by molecular beam epitaxy

Ternary chalcogenides such as the parkerites and shandites are a broad class of materials exhibiting rich diversity of transport and magnetic behavior as well as an array of topological phases including Weyl and Dirac nodes. However, they remain largely unexplored as high-quality epitaxial thin films. Here, we report the self-regulated growth of thin films of the strong spin-orbit coupled superconductor Pd3Bi2Se2 on SrTiO3 by molecular beam epitaxy. Films are found to grow in a self-regulated fashion, where, in excess Se, the temperature and relative flux ratio of Pd to Bi controls the formation of Pd3Bi2Se2 due to the combined volatility of Bi, Se, and Bi-Se bonded phases. The resulting films are shown to be of high structural quality, the stoichiometry is independent of the Pd:Bi and Se flux ratio and exhibit a superconducting transition temperature of 800 mK and critical field of 17.7 +/- 0.5 mT, as probed by transport as well as magnetometry. Understanding and navigating the growth of the chemically and structurally diverse classes of ternary chalcogenides opens a vast space for discovering new phenomena as well as enabling new applications.

cond-mat.mtrl-sci↗

arXiv2021

Correlated Oxide Dirac Semimetal in the Extreme Quantum Limit

Quantum materials (QMs) with strong correlation and non-trivial topology are indispensable to next-generation information and computing technologies. Exploitation of topological band structure is an ideal starting point to realize correlated topological QMs. Herein, we report that strain-induced symmetry modification in correlated oxide SrNbO3 thin films creates an emerging topological band structure. Dirac electrons in strained SrNbO3 films reveal ultra-high mobility (100,000 cm2/Vs), exceptionally small effective mass (0.04me), and non-zero Berry phase. More importantly, strained SrNbO3 films reach the extreme quantum limit, exhibiting a sign of fractional occupation of Landau levels and giant mass enhancement. Our results suggest that symmetry-modified SrNbO3 is a rare example of a correlated topological QM, in which strong correlation of Dirac electrons leads to the realization of fractional occupation of Landau levels.

cond-mat.str-el↗

arXiv2021

Damped Dirac magnon in a metallic kagome antiferromagnet FeSn

The kagome lattice is a fertile platform to explore topological excitations with both Fermi-Dirac and Bose-Einstein statistics. While relativistic Dirac Fermions and flat-bands have been discovered in the electronic structure of kagome metals, the spin excitations have received less attention. Here we report inelastic neutron scattering studies of the prototypical kagome magnetic metal FeSn. The spectra display well-defined spin waves extending up to 120 meV. Above this energy, the spin waves become progressively broadened, reflecting interactions with the Stoner continuum. Using linear spin wave theory, we determine an effective spin Hamiltonian that reproduces the measured dispersion. This analysis indicates that the Dirac magnon at the K-point remarkably occurs on the brink of a region where well-defined spin waves become unobservable. Our results emphasize the influential role of itinerant carriers on the topological spin excitations of metallic kagome magnets.

cond-mat.str-el↗

arXiv2021

Van der Waals Epitaxy on Freestanding Monolayer Graphene Membrane by MBE

Research on two-dimensional materials has expanded over the past two decades to become a central theme in condensed matter research today. Significant advances have been made in the synthesis and subsequent reassembly of these materials using mechanical methods into a vast array of hybrid structures with novel properties and ever-increasing potential applications. The key hurdles in realizing this potential are the challenges in controlling the atomic structure of these layered hybrid materials and the difficulties in harnessing their unique functionality with existing semiconductor nanofabrication techniques. Here we report on high-quality van der Waals epitaxial growth and characterization of a layered topological insulator on freestanding monolayer graphene transferred to different mechanical supports. This templated synthesis approach enables direct interrogation of interfacial atomic structure of these as-grown hybrid structures and opens a route towards creating device structures with more traditional semiconductor nanofabrication techniques.

cond-mat.mtrl-sci↗

arXiv2021

On the Spatial Locality of Electronic Correlations in LiFeAs

We address the question of the degree of spatial non-locality of the self energy in the iron-based superconductors, a subject which is receiving considerable attention. Using LiFeAs as a prototypical example, we extract the self energy from angular-resolved photoemission spectroscopy (ARPES) data. We use two distinct electronic structure references: density functional theory in the local density approximation and linearized quasiparticle self consistent GW (LQSGW). We find that with the LQSGW reference, spatially local dynamical correlations provide a consistent description of the experimental data, and account for some surprising aspects of the data such as the substantial out of plan dispersion of the electron Fermi surface having dominant xz/yz character. Hence, correlations effects can be separated into static non-local contributions well described by LQSGW and dynamical local contributions. Hall effect and resistivity data are shown to be consistent with this description.

cond-mat.str-el↗

arXiv2020

Strong spin-dephasing in a topological insulator - paramagnet heterostructure

The interface between magnetic materials and topological insulators can drive the formation of exotic phases of matter and enable functionality through manipulation of the strong spin polarized transport. Here, we report that the spin-momentum-locked transport in the topological insulator Bi$_2$Se$_3$ is completely suppressed by scattering at a heterointerface with the kagome-lattice paramagnet, Co$_7$Se$_8$. Bi$_2$Se$_{3-}$Co$_7$Se$_{8-}$Bi$_2$Se$_3$ trilayer heterostructures were grown using molecular beam epitaxy. Magnetotransport measurements revealed a substantial suppression of the weak antilocalization effect for Co$_7$Se$_8$ at thicknesses as thin as a monolayer, indicating a strong dephasing mechanism. Bi$_{2-x}$Co$_x$Se$_3$ films, where Co is in a non-magnetic $3^+$ state, show weak antilocalization that survives to $x = 0.5$, which, in comparison with the heterostructures, suggests the unordered moments of the Co$^{2+}$ act as a far stronger dephasing element. This work highlights several important points regarding spin-polarized transport in topological insulator interfaces and how magnetic materials can be integrated with topological materials to realize both exotic phases as well as novel device functionality.

cond-mat.mtrl-sci↗

arXiv2019

Quantum phase transition of correlated iron-based superconductivity in LiFe$_{1-x}$Co$_x$As

The interplay between unconventional Cooper pairing and quantum states associated with atomic scale defects is a frontier of research with many open questions. So far, only a few of the high-temperature superconductors allow this intricate physics to be studied in a widely tunable way. We use scanning tunneling microscopy (STM) to image the electronic impact of Co atoms on the ground state of the LiFe$_{1-x}$Co$_x$As system. We observe that impurities progressively suppress the global superconducting gap and introduce low energy states near the gap edge, with the superconductivity remaining in the strong-coupling limit. Unexpectedly, the fully opened gap evolves into a nodal state before the Cooper pair coherence is fully destroyed. Our systematic theoretical analysis shows that these new observations can be quantitatively understood by the nonmagnetic Born-limit scattering effect in a s$\pm$-wave superconductor, unveiling the driving force of the superconductor to metal quantum phase transition.

cond-mat.supr-con↗

arXiv2018

Imaging antiferromagnetic antiphase domain boundaries using magnetic Bragg diffraction phase contrast

Manipulating magnetic domains is essential for many technological applications. Recent breakthroughs in Antiferromagnetic Spintronics brought up novel concepts for electronic device development. Imaging antiferromagnetic domains is of key importance to this field. Unfortunately, some of the basic domain types, such as antiphase domains, cannot be imaged by conventional techniques. Herein, we present a new domain projection imaging technique based on the localization of domain boundaries by resonant magnetic diffraction of coherent x rays. Contrast arises from reduction of the scattered intensity at the domain boundaries due to destructive interference effects. We demonstrate this approach by imaging antiphase domains in a collinear antiferromagnet Fe2Mo3O8, and observe evidence of domain wall interaction with a structural defect. This technique does not involve any numerical algorithms. It is fast, sensitive, produces large-scale images in a single-exposure measurement, and is applicable to a variety of magnetic domain types.

cond-mat.mes-hall↗