arXiv subjects

Nojoon Myoung

Publications and source records attributed to Nojoon Myoung.

25 records · Page 2Linked to original sources

arXiv2017

Conductance oscillations in Chern insulator junctions: valley-isospin dependence and Aharonov-Bohm effects

The transport properties of Chern insulator junctions generated by bipolar junctions in quantum Hall graphene are theoretically studied in the coherent regime. Coherent transport across the junction exhibits two mesoscopic features: valley-isospin dependence of the quantum Hall conductance, and the Aharonov-Bohm (AB) effects with the interface channels. We demonstrate that the valley-isospin dependence can be measured in a graphene sample with perfect edge terminations, resulting in conductance oscillation for the smallest Chern number case. On the other hand, while conductance plateaus are found to be unclear for larger Chern numbers, the conductance exhibits an oscillatory behavior of which period is relatively longer than the valley-isospin dependent oscillation. This conductance oscillation is ascribed to the AB effect, which is implicitly created by the split metallic channels near the junction interface. We point out that a possible origin of the unclear plateaus previously speculated to be incompleteness in realistic devices is the low-visibility conductance oscillation due to unequal beam splitting.

cond-mat.mes-hall↗

arXiv2017

Antiresonance induced by symmetry-broken contacts in quasi-one-dimensional lattices

We report the effect of symmetry-broken contacts on quantum transport in quasi-one-dimensional lattices. In contrast to 1D chains, transport in quasi-one-dimensional lattices, which are made up of a finite number of 1D chain layers, is strongly influenced by contacts. Contact symmetry depends on whether the contacts maintain or break the parity symmetry between the layers. With balanced on-site potential, a flat band can be detected by asymmetric contacts, but not by symmetric contacts. In the case of asymmetric contacts with imbalanced on-site potential, transmission is suppressed at certain energies. We elucidate these energies of transmission suppression related to antiresonance using reduced lattice models and Feynman paths. These results provide a nondestructive measurement of flat band energy which it is difficult to detect.

cond-mat.mes-hall↗

arXiv2017

Reconfiguration of quantum states in $\mathcal PT$-symmetric quasi-one dimensional lattices

We demonstrate mesoscopic transport through quantum states in quasi-1D lattices maintaining the combination of parity and time-reversal symmetries by controlling energy gain and loss. We investigate the phase diagram of the non-Hermitian system where transitions take place between unbroken and broken $\mathcal{PT}$-symmetric phases via exceptional points. Quantum transport in the lattice is measured only in the unbroken phases in the energy band-but not in the broken phases. The broken phase allows for spontaneous symmetry-broken states where the cross-stitch lattice is separated into two identical single lattices corresponding to conditionally degenerate eigenstates. These degeneracies show a lift-up in the complex energy plane, caused by the non-Hermiticity with $\mathcal{PT}$-symmetry.

quant-ph↗

arXiv2015

Gate-Tunable Spin Transport and Giant Electroresistance in Ferromagnetic Graphene Vertical Heterostructures

We investigate spin transport through ferromagnetic graphene vertical heterostructures where a sandwiched tunneling layer is either a normal or ferroelectric insulator. We show that the spin-polarization of the tunneling current is electronically controlled via gate voltages. We also demonstrate that the tunneling current of Dirac fermions can be prohibited when the spin configuration of ferromagnetic graphene sheets is opposite. The giant electroresistance can thus be developed by using the proposed heterostructure in this study. The effects of temperature on the spin transport and the giant electroresistance ratio are also investigated. Our findings discover the prospect of manipulating the spin transport properties in vertical heterostructures through an electric fields via gate and bias electrodes.

cond-mat.mes-hall↗

arXiv2015

Highly Sensitive Gas and Temperature Sensor Based on Conductance Modulation in Graphene with Multiple Magnetic Barriers

The electronic and transport properties of graphene modulated by magnetic barrier arrays are derived for finite temperature. Prominent conductance gaps, originating from quantum interference effects are found in the periodic array case. When a structural defect is inserted in the array, sharp defect modes of high conductance appear within the conductance gaps. These modes can be shifted by local doping in the defect region resulting into sensing of the chemical molecules that adhere on the graphene sheet. In general it is found that sensitivity is strongly dependent on temperature due to smoothing out of the defect-induced peaks and transport gaps. This temperature dependence, however, offers the added capability for sub-mK temperature sensing resolution, and thus an opportunity towards ultra-sensitive combined electrochemical-calorimetric sensing.

cond-mat.mes-hall↗

arXiv2014

Valley-dependent resonant tunneling through double magnetic barriers in suspended graphene

We theoretically investigate the effects of strain-induced pseudomagnetic fields on the transmission probability and the ballistic conductance for Dirac fermion transport in suspended graphene. We show that resonant tunneling through double magnetic barriers can be tuned by strain in the suspended region. The valley-resolved transmission peaks are apparently distinguishable owing to the sharpness of the resonant tunneling. With the specific strain, the resonant tunneling is completely suppressed for Dirac fermions occupying the one valley, but the resonant tunneling exists for the other valley. The valley-filtering effect is expected to be measurable by strain engineering. The proposed system can be used to fabricate a graphene valley filter with the large valley polarization almost 100%.

cond-mat.mes-hall↗

arXiv2013

Large Current Modulation and Spin-Dependent Tunneling of Vertical Graphene/MoS$_{2}$ Heterostructures

Vertical graphene heterostructures have been introduced as an alternative architecture for electronic devices by using quantum tunneling. Here, we present that the current on/off ratio of vertical graphene field-effect transistors is enhanced by using an armchair graphene nanoribbon as an electrode. Moreover, we report spin-dependent tunneling current of the graphene/MoS2 heterostructures. When an atomically thin MoS2 layer sandwiched between graphene electrodes becomes magnetic, Dirac fermions with different spins feel different height of the tunnel barrier, leading to spin-dependent tunneling. Our finding will develop the present graphene heterostructures for electronic devices by improving the device performance and by adding the possibility of spintronics based on graphene.

cond-mat.mes-hall↗