arXiv subjects

Noah F. Q. Yuan

Publications and source records attributed to Noah F. Q. Yuan.

40 records · Page 3Linked to original sources

arXiv2015

Generating Giant Spin Currents Using Nodal Topological Superconductors

In this work, we show that a giant spin current can be injected into a nodal topological superconductor, using a normal paramagnetic lead, through a large number of zero energy Majorana fermions at the superconductor edge. The giant spin current is caused by the selective equal spin Andreev reflections (SESAR) induced by Majorana fermions. In each SESAR event, a pair of electrons with certain spin polarization are injected into the nodal topological superconductor, even though the pairing in the bulk of the nodal superconductor is spin-singlet s-wave. We further explain the origin of the spin current by showing that the pairing correlation at the edge of a nodal topological superconductor is predominantly equal spin-triplet at zero energy. The experimental consequences of SESAR in nodal topological superconductors are discussed.

cond-mat.supr-con↗

arXiv2015

Two Dimensional Ising Superconductivity in Gated MoS$_{2}$

The Zeeman effect, which is usually considered to be detrimental to superconductivity, can surprisingly protect the superconducting states created by gating a layered transition metal dichalcogenide. This effective Zeeman field, which is originated from intrinsic spin orbit coupling induced by breaking in-plane inversion symmetry, can reach nearly a hundred Tesla in magnitude. It strongly pins the spin orientation of the electrons to the out-of-plane directions and protects the superconductivity from being destroyed by an in-plane external magnetic field. In magnetotransport experiments of ionic-gate MoS$_{2}$ transistors, where gating prepares individual superconducting state with different carrier doping, we indeed observe a spin- protected superconductivity by measuring an in-plane critical field $\textit{B}$$_{c2}$ far beyond the Pauli paramagnetic limit. The gating-enhanced $\textit{B}$$_{c2}$ is more than an order of magnitude larger compared to the bulk superconducting phases where the effective Zeeman field is weakened by interlayer coupling. Our study gives the first experimental evidence of an Ising superconductor, in which spins of the pairing electrons are strongly pinned by an effective Zeeman field.

cond-mat.supr-con↗

arXiv2014

Possible Topological Superconducting Phases of MoS$_{2}$

Molybdenum disulphide (MoS$_2$) has attracted much interest in recent years due to its potential applications in a new generation of electronic devices. Recently, it was shown that thin films of MoS$_2$ can become superconducting with a highest $T_{c}$ of 10K when the material is heavily gated to the conducting regime. In this work, using the group theoretical approach, we determine the possible pairing symmetries of heavily gated MoS$_2$. Depending on the electron-electron interactions, the material can support an exotic spin-singlet $p +ip $-wave-like, an exotic spin-triplet s-wave-like and an conventional spin-triplet $p$-wave pairing phases. Importantly, the exotic spin-singlet $p+ip$-wave phase is a topological superconducting phase which breaks time-reversal symmetry spontaneously and possesses chiral Majorana edge states.

cond-mat.supr-con↗

arXiv2013

Probing Majorana Flat Bands in Nodal $d_{x^2-y^2}$-wave Superconductors with Rashba Spin-Orbit Coupling

We show that Majorana fermions associated with Majorana flat bands emerge as zero energy modes on the [110] edge of single layer or multilayer nodal superconductors with $d_{x^2-y^2}$-wave pairing and Rashba spin-orbit coupling. Moreover, as long as the global inversion symmetry of the single layer or multilayer superconductor is broken, and in the presence of an in-plane magnetic field parallel to the [110] edge, the Majorana fermions together with usual fermionic Andreev bound states induce a triple-peak structure in tunnelling spectroscopy experiments. Importantly, we show that the zero bias conductance peak is induced by Majorana fermions. Therefore, tunnelling spectroscopy can be used to probe Majorana fermions in nodal $d_{x^2-y^2}$-wave superconductors.

cond-mat.supr-con↗