arXiv subjects

Donghao Liu

Publications and source records attributed to Donghao Liu.

16 recordsLinked to original sources

arXiv2026

Conductance Anomaly in a Partially Open Adiabatic Quantum Point Contact

We demonstrate that conductance anomalies can arise in a clean, adiabatic quantum point contact when a channel is partially transmitting. Even for a smooth barrier potential, backscattering induces Friedel oscillations that, via electron interactions, generate a singular correction to the conductance. This correction is maximized when the channel is half-open, resulting in a reduction of conductance. In addition, a magnetic field applied perpendicular to the spin-orbit axis modifies the single-particle spectrum, resulting in conductance oscillations via Fabry-Pérot-type interference, as well as a non-monotonic field dependence of the anomaly. Our findings reveal a universal mechanism by which interactions modify the conductance of an ideal partially open channel and offer a possible explanation for the anomalous features observed in experiments.

cond-mat.mes-hall↗

arXiv2023

Elementary models of 3D topological insulators with chiral symmetry

We construct a set of lattice models of non-interacting topological insulators with chiral symmetry in three dimensions. We build a model of the topological insulators in the class AIII by coupling lower dimensional models of $\mathbb{Z}$ classes. By coupling the two AIII models related by time-reversal symmetry we construct other chiral symmetric topological insulators that may also possess additional symmetries (the time-reversal and/or particle-hole). There are two different chiral symmetry operators for the coupled model, that correspond to two distinct ways of defining the sublattices. The integer topological invariant (the winding number) in case of weak coupling can be either the sum or difference of indices of the basic building blocks, dependent on the preserved chiral symmetry operator. The value of the topological index in case of weak coupling is determined by the chiral symmetry only and does not depend on the presence of other symmetries. For $\mathbb{Z}$ topological classes AIII, DIII, and CI with chiral symmetry are topologically equivalent, it implies that a smooth transition between the classes can be achieved if it connects the topological sectors with the same winding number. We demonstrate this explicitly by proving that the gapless surface states remain robust in $\mathbb{Z}$ classes as long as the chiral symmetry is preserved, and the coupling does not close the gap in the bulk. By studying the surface states in $\mathbb{Z}_2$ topological classes, we show that class CII and AII are distinct, and can not be adiabatically connected.

cond-mat.mes-hall↗

arXiv2022

One-dimensional non-interacting topological insulators with chiral symmetry

We construct microscopical models of one-dimensional non-interacting topological insulators in all of the chiral universality classes. Specifically, we start with a deformation of the Su-Schrieffer-Heeger (SSH) model that breaks time-reversal symmetry, which is in the AIII class. We then couple this model to its time-reversal counterpart in order to build models in the classes BDI, CII, DIII and CI. We find that the $\mathbb{Z}$ topological index (the winding number) in individual chains is defined only up to a sign. This comes from noticing that changing the sign of the chiral symmetry operator changes the sign of the winding number. The freedom to choose the sign of the chiral symmetry operator on each chain independently allows us to construct two distinct possible chiral symmetry operators when the chains are weakly coupled -- in one case, the total winding number is given by the sum of the winding number of individual chains while in the second case, the difference is taken. We find that the chiral models that belong to $\mathbb{Z}$ classes, AIII, BDI and CII are topologically equivalent, so they can be adiabatically deformed into one another so long as the chiral symmetry is preserved. We study the properties of the edge states in the constructed models and prove that topologically protected edge states must all be localised on the same sublattice (on any given edge). We also discuss the role of particle-hole symmetry on the protection of edge states and explain how it manages to protect edge states in $\mathbb{Z}_2$ classes, where the integer invariant vanishes and chiral symmetry alone does not protect the edge states anymore. We discuss applications of our results to the case of an arbitrary number of coupled chains, construct possible chiral symmetry operators for the multiple chain case, and briefly discuss the generalisation to any odd number of dimensions.

cond-mat.mes-hall↗

arXiv2022

Large Andreev bound state zero bias peaks in a weakly dissipative environment

We study Andreev bound states in hybrid InAs-Al nanowire devices. The energy of these states can be tuned to zero by gate voltage or magnetic field, revealing large zero bias peaks (ZBPs) near 2e^2/h in tunneling conductance. Probing these large ZBPs using a weakly dissipative lead reveals non-Fermi liquid temperature (T) dependence due to environmental Coulomb blockade (ECB), an interaction effect from the lead acting on the nanowire junction. By increasing T, these large ZBPs either show a height increase or a transition from split peaks to a ZBP, both deviate significantly from non-dissipative devices where a Fermi-liquid T dependence is revealed. Our result demonstrates the competing effect between ECB and thermal broadening on Andreev bound states.

cond-mat.mes-hall↗

arXiv2022

Double Fu-teleportation and anomalous Coulomb blockade in a Majorana-hosted superconducting island

We study the temperature dependence of Coulomb Blockade peak conductance based on a Majorana-hosted superconducting island. In the low-temperature regime, we discover a coherent double Fu-teleportation (FT) process, where any independent tunneling process always involves two coherent FTs; and we also find an anomalous universal scaling behavior, which shows a transition from a [max(T,eV)]^6 to a [max(T,eV)]^3 conductance behavior as increasing energy scale. In the high-temperature regime, using the familiar rate equation method, we find that the conductance is proportional to the reciprocal of the temperature and shows a non-monotonic temperature-dependence. Both the anomalous power-law behavior and non-monotonic temperature-dependence can be distinguished from the conductance peak in the traditional Coulomb block, and therefore, serve as a hallmark for the non-local transport in the topological superconducting island.

cond-mat.mes-hall↗

arXiv2021

Universal conductance scaling of Andreev reflections using a dissipative probe

The Majorana search is caught up in an extensive debate about the false-positive signals from non-topological Andreev bound states (ABSs). We introduce a remedy using the dissipative probe to generate electron-boson interaction. We theoretically show that the interaction-induced renormalization leads to significantly distinct universal zero-bias conductance behaviors, i.e. distinct characteristic power-law in temperature, for different types of Andreev reflections, which shows a sharp contrast to that of a Majorana zero mode. Various specific cases have been studied, including the cases that two charges involved in an Andreev reflection process maintain/lose coherence, and the cases for multiple ABSs with or without a Majorana present. A transparent list of conductance features in each case is provided to help distinguishing the observed subgap states in experiments, which also promotes the identification of Majorana zero modes.

cond-mat.mes-hall↗

arXiv2021

Suppressing Andreev bound state zero bias peaks using a strongly dissipative lead

Hybrid semiconductor-superconductor nanowires are predicted to host Majorana zero modes, manifested as zero-bias peaks (ZBPs) in tunneling conductance. ZBPs alone, however, are not sufficient evidence due to the ubiquitous presence of Andreev bound states in the same system. Here, we implement a strongly resistive normal lead in our InAs-Al nanowire devices and show that most of the expected ZBPs, corresponding to zero-energy Andreev bound states, can be suppressed, a phenomenon known as environmental Coulomb blockade. Our result is the first experimental demonstration of this dissipative interaction effect on Andreev bound states and can serve as a possible filter to narrow down ZBP phase diagram in future Majorana searches.

cond-mat.mes-hall↗

arXiv2021

Large zero bias peaks and dips in a four-terminal thin InAs-Al nanowire device

We report electron transport studies of a thin InAs-Al hybrid semiconductor-superconductor nanowire device using a four-terminal design. Compared to previous works, thinner InAs nanowire (diameter less than 40 nm) is expected to reach fewer sub-band regime. The four-terminal device design excludes electrode contact resistance, an unknown value which has inevitably affected previously reported device conductance. Using tunneling spectroscopy, we find large zero-bias peaks (ZBPs) in differential conductance on the order of $2e^2/h$. Investigating the ZBP evolution by sweeping various gate voltages and magnetic field, we find a transition between a zero-bias peak and a zero-bias dip while the zero-bias conductance sticks close to $2e^2/h$. We discuss a topologically trivial interpretation involving disorder, smooth potential variation and quasi-Majorana zero modes.

cond-mat.mes-hall↗

arXiv2021

Fast Camera Image Denoising on Mobile GPUs with Deep Learning, Mobile AI 2021 Challenge: Report

Image denoising is one of the most critical problems in mobile photo processing. While many solutions have been proposed for this task, they are usually working with synthetic data and are too computationally expensive to run on mobile devices. To address this problem, we introduce the first Mobile AI challenge, where the target is to develop an end-to-end deep learning-based image denoising solution that can demonstrate high efficiency on smartphone GPUs. For this, the participants were provided with a novel large-scale dataset consisting of noisy-clean image pairs captured in the wild. The runtime of all models was evaluated on the Samsung Exynos 2100 chipset with a powerful Mali GPU capable of accelerating floating-point and quantized neural networks. The proposed solutions are fully compatible with any mobile GPU and are capable of processing 480p resolution images under 40-80 ms while achieving high fidelity results. A detailed description of all models developed in the challenge is provided in this paper.

eess.IV↗

arXiv2021

NBNet: Noise Basis Learning for Image Denoising with Subspace Projection

In this paper, we introduce NBNet, a novel framework for image denoising. Unlike previous works, we propose to tackle this challenging problem from a new perspective: noise reduction by image-adaptive projection. Specifically, we propose to train a network that can separate signal and noise by learning a set of reconstruction basis in the feature space. Subsequently, image denosing can be achieved by selecting corresponding basis of the signal subspace and projecting the input into such space. Our key insight is that projection can naturally maintain the local structure of input signal, especially for areas with low light or weak textures. Towards this end, we propose SSA, a non-local subspace attention module designed explicitly to learn the basis generation as well as the subspace projection. We further incorporate SSA with NBNet, a UNet structured network designed for end-to-end image denosing. We conduct evaluations on benchmarks, including SIDD and DND, and NBNet achieves state-of-the-art performance on PSNR and SSIM with significantly less computational cost.

cs.CV↗

arXiv2020

Topological Kondo Device for distinguishing Quasi-Majorana and Majorana signatures

To confirm the Majorana signatures, significant effort has been devoted to distinguishing between Majorana zero modes (MZMs) and spatially separated quasi-Majorana modes (QMMs). Because both MZMs and QMMs cause a quantized zero-bias peak in the conductance measurement, their verification task is thought to be very difficult. Here, we proposed a simple device with a single nanowire, where the device could develop clear evidence of the topological Kondo effect in the topologically trivial phase with four QMMs. On the other hand, in the topological superconducting phase with MZMs, the transport signatures are significantly different. Therefore, our scheme provides a simple way to distinguish Majorana and quasi-Majorana modes.

cond-mat.mes-hall↗

arXiv2020

The Tianlai Cylinder Pathfinder Array: System Functions and Basic Performance Analysis

The Tianlai Cylinder Pathfinder is a radio interferometer array designed to test techniques for 21 cm intensity mapping in the post-reionization Universe, with the ultimate aim of mapping the large scale structure and measuring cosmological parameters such as the dark energy equation of state. Each of its three parallel cylinder reflectors is oriented in the north-south direction, and the array has a large field of view. As the Earth rotates, the northern sky is observed by drift scanning. The array is located in Hongliuxia, a radio-quiet site in Xinjiang, and saw its first light in September 2016. In this first data analysis paper for the Tianlai cylinder array, we discuss the sub-system qualification tests, and present basic system performance obtained from preliminary analysis of the commissioning observations during 2016-2018. We show typical interferometric visibility data, from which we derive the actual beam profile in the east-west direction and the frequency band-pass response. We describe also the calibration process to determine the complex gains for the array elements, either using bright astronomical point sources, or an artificial on site calibrator source, and discuss the instrument response stability, crucial for transit interferometry. Based on this analysis, we find a system temperature of about 90 K, and we also estimate the sensitivity of the array.

astro-ph.IM↗

arXiv2020

Determining the Superconducting Transition Temperatures of Liquids

We develop a non-perturbative approach for calculating the superconducting transition temperatures ($T_{c}$) of liquids. The electron-electron scattering amplitude induced by electron-phonon coupling (EPC), from which the effective pairing interaction can be inferred, is related to the fluctuation of the $T$-matrix of electron scattering induced by ions. By applying the relation, EPC parameters can be extracted from a path-integral molecular dynamics simulation. For determining $T_{c}$, the linearized Eliashberg equations are re-established in the non-perturbative context. We apply the approach to estimate $T_{c}$ of metallic hydrogen liquids. It indicates that metallic hydrogen liquids in the pressure regime from $0.5$ to $1.5\mathrm{\,TPa}$ have $T_{c}$ well above their melting temperatures, therefore are superconducting liquids.

cond-mat.supr-con↗

arXiv2019

Reveal the non-local coherent nature from a dissipative Majorana teleportation

The non-local coherent nature of the Majorana devices is one of the key factors for realizing decoherence-free topological qubits. Direct observation of this coherent nature could provide a first-step benchmarking scheme to validate Majorana qubit quality. We propose a simple transport scheme with a Majorana island device along with a dissipative environment in the electrodes. We found that the dissipative environment renormalizes the quantum transport in significant different ways: As reducing temperature, while the conductance for Majorana coherent teleportation increases, all other incoherent signals are strongly suppressed due to dissipation. This special conductance scaling behavior is a clear benchmark to reveal the non-local coherent nature of Majorana devices.

cond-mat.mes-hall↗

arXiv2018

Circular phonon dichroism in Weyl semimetals

We derive the phonon dynamics of magnetic metals in the presence of strong spin-orbit coupling. We show that both a dissipationless viscosity and a dissipative viscosity arise in the dynamics. While the dissipationless viscosity splits the dispersion of left-handed and right-handed circularly polarized phonons, the dissipative viscosity damps them differently, inducing circular phonon dichroism. The effect offers a new degree of manipulation of phonons, i.e., the control of the phonon polarization. We investigate the effect in Weyl semimetals. We find that there exists strong circular phonon dichroism in Weyl semimetals breaking both the time-reversal and the inversion symmetry, making them potential materials for realizing the acoustic circular polarizer.

cond-mat.mes-hall↗

arXiv2015

Antenna system characteristic and solar radio burst observation

Chinese Spectral Radio Heliograph (CSRH) is an advanced aperture synthesis solar radio heliograph, developed by National Astronomical Observatories, Chinese Academy of Sciences independently. It consists of 100 reflector antennas, which are grouped into two antenna arrays (CSRH-I and CSRH-II) for low and high frequency bands respectively. The frequency band of CSRH-I is 0.4-2GHz and for CSRH-II, the frequency band is 2-15GHz. In the antenna and feed system, CSRH uses an Eleven feed to receive signals coming from the Sun, the radiation pattern with lower side lobe and back lobe of the feed is well radiated. The characteristics of gain G and antenna noise temperature T effect the quality of solar radio imaging. For CSRH, measured G is larger than 60 dBi and $ T $ is less than 120K, after CSRH-I was established, we have successfully captured a solar radio burst between 1.2-1.6GHz on November 12, 2010 through this instrument and this event was confirmed through the observation of Solar Broadband Radio Spectrometer (SBRS) at 2.84GHz and Geostationary Operational Environmental Satellite (GOES). In addition, an image obtained from CSRH-I clearly reveals the profile of the solar radio burst. The other observational work is the imaging of Fengyun-2E geosynchronous satellite which is assumed to be a point source. This data processing method indicates that, the method of deleting errors about dirty image could be used for processing other surface sources.

astro-ph.IM↗