Jianqiang Hou

Achieving Ultrahigh Carrier Mobility in Two-Dimensional Hole Gas of Black Phosphorus

We demonstrate that a field effect transistor (FET) made of few layer black phosphorus (BP) encapsulated in hexagonal boron nitride (h-BN) in vacuum, exhibts the room temperature hole mobility of 5200 cm 2 /Vs being limited just by the phonon scattering. At cryogenic tempeature the FET mobility increases up to 45,000 cm 2 /Vs, which is eight times higher compared with the mobility obtained in earlier reports. The unprecedentedly clean h-BN/BP/h-BN heterostructure exhibits Shubnikov-de Haas oscillations and quantum Hall effect with Landau level (LL) filling factors down to v=2 in conventional laboratory magnetic fields. Moreover, carrier density independent effective mass m=0.26 m0 is

Odd-Integer Quantum Hall States and Giant Spin Susceptibility in p -Type Few-Layer WSe2

We fabricate high-mobility p-type few-layer WSe_{2} field-effect transistors and surprisingly observe a series of quantum Hall (QH) states following an unconventional sequence predominated by odd-integer states under a moderate strength magnetic field. By tilting the magnetic field, we discover Landau level crossing effects at ultralow coincident angles, revealing that the Zeeman energy is about 3 times as large as the cyclotron energy near the valence band top at the Γ valley. This result implies the significant roles played by the exchange interactions in p-type few-layer WSe_{2}, in which itinerant or QH ferromagnetism likely occurs. Evidently, the Γ valley of few-layer WSe_{2} offers a unique platform with unusually heavy hole carriers and a substantially enhanced g factor for exploring strongly correlated phenomena.

Type-controlled Nanodevices Based on Encapsulated Few-layer Black Phosphorus for Quantum Transport

We demonstrate that encapsulation of atomically thin black phosphorus (BP) by hexagonal boron nitride (h-BN) sheets is very effective for minimizing the interface impurities induced during fabrication of BP channel material for quantum transport nanodevices. Highly stable BP nanodevices with ultrahigh mobility and controllable types are realized through depositing appropriate metal electrodes after conducting a selective etching to the BP encapsulation structure. Chromium and titanium are suitable metal electrodes for BP channels to control the transition from a p-type unipolar property to ambipolar characteristic because of different work functions. Record-high mobilities of 6000 cm2 V−1 s−1 and 8400 cm2 V−1 s−1 are respectively obtained for electrons and holes at cryogenic temperatures. High-mobility BP devices enable the investigation of quantum oscillations with an indistinguishable Zeeman effect in laboratory magnetic field.

Absence of Nematic Order in the Pressure-induced Intermediate Phase of the Iron-based Superconductor Ba 0.85 K 0.15 Fe 2 As 2

The hole doped Fe-based superconductors Ba1-xAxFe2As2 (where A=Na or K) show a particular rich phase diagram. It was observed that an intermediate re-entrant tetragonal phase forms within the orthorhombic antiferromagnetically-ordered stripe-type spin density wave state above the superconducting transition [S. Avci et al., Nature Comm. 5, 3845 (2014), A. E. Böhmer et al., arXiv:1412.7038v2]. A similar intermediate phase was reported to appear if pressure is applied to underdoped Ba1-xKxFe2As2 [E. Hassinger et al., Phys. Rev. B 86, 140502(R) (2012)]. Here we report data of the electric resistivity, Hall effect, specific heat, and the thermoelectrical Nernst and Seebeck coefficients measured on a Ba0.85K0.15Fe2As2 single crystal under pressure up to 5.5 GPa. The data reveals a coexistence of the intermediate phase with filamentary superconductivity. The Nernst coefficient shows a large signature of nematic order that coincides with the stripe-type spin density wave state up to optimal pressure. In the pressure-induced intermediate phase the nematic order is removed, thus confirming that its nature is a reentrant tetragonal phase.

Doping dependence of the critical fluctuation regime in the Fe-based superconductor Ba1-xKxFe2As2

We investigate the importance of superconducting order parameter fluctuations in the 122 family of Fe-based superconductors, using high-resolution specific heat and thermal expansion data of various Ba

Strong-coupling phonon-mediated scenario of superconductivity in Ca3Ir4Sn13 and Ca-3( Ir0.91Co0.09)(4)Sn-13

_{1-x}

Possible Coexistence of Double-Q Magnetic Order and Chequerboard Charge Order in the Re-entrant Tetragonal Phase of Ba 0.76 K 0.24 Fe 2 As 2

K

Spin reorientation and 'quasi-nematic' order in the re-entrant tetragonal phase of Ba

_x

_{0.76}

Fe

K

_2