Modulation-doped-semiconductorlike behavior manifested in magnetotransport measurements ofLixZrNCllayered superconductors

Abstract

Transport properties in magnetic fields have been investigated for possibly exotic Li x ZrNCl superconductors with a wide range of doping concentration of 0.06ഛ x ഛ 0.37. Application of magnetic field along c axis rapidly suppressed the superconducting transition temperature ͑T c ͒ while strongly broadening the width. Zerotemperature limit of upper critical field ͓H c2 ͑0͔͒ showed systematic and monotonic decrease upon increasing x. Detailed analysis with a phenomenological argument gave a simple relation of k F L ϰ x and almost x-independent ͑k F , L, and denote Fermi wave number, mean free path, and carrier mobility, respectively͒. These results combined with the temperature-independent Hall coefficient clearly indicate that the present system can be viewed as modulation-doped semiconductors in which conduction electrons suffer from minimal disorder scattering. This could be a key to the relatively high-T c values realized in this class of layered superconductors.

Superconductivity in layered nitride with small carrier density

“…We used pellets with a high degree of c-axis orientation by compressing the powder which is composed of fine particles with highly anisotropic plate-like shape. The distribution of the c-axis orientation was revealed to be within ±5°by rocking curve experiment, in accord with previous reports [13,20,29]. We applied the magnetic field along the c axis in all the measurements.…”

“…3 shows the temperature ðTÞ dependence of electronic part of the specific heat ðCÞ divided by T; DC=T, for Li x ZrNCl with x ¼ 0:10 and 0.28, respectively [30]. We estimated the electronic part of specific heat as DCðH; TÞ ½CðH; TÞ À CðH > H c2 ; TÞ, where H c2 is the upper critical field [21,29]. In zero magnetic field, jump of the specific heat is clearly discernible at T c .…”

Unconventional superconductivity in electron-doped layered metal nitride halides MNX (M= Ti, Zr, Hf; X= Cl, Br, I)

“…In fact, from systematic experiments for various samples with different doping concentrations in combination with phenomenological consideration, it was conjectured that the intrinsic value of the resistivity for a single crystal without any grain boundary scattering would be smaller than the observed value by almost two orders of magnitude [21]. Also, intrinsic mobility values of carriers at low temperatures were estimated to be between 65 and 110 cm 2 /Vs [21] for a wide range of doping concentration Figure 4: N 1s X-ray absorption spectra of (a) β-HfNCl and (b) Na 0.22 HfNCl in the total fluorescence mode. Measurement configuration is displayed as an inset, and θ denotes incident angle of the X-ray with respect to the sample normal.…”

Dielectric response of electron-doped ionic superconductorLixZrNCl

“…First, and an aspect that is not usually emphasized, they are extremely bad conductors, with reported residual resistivity (T→0) of 10 3 −10 5 µΩ cm. 4,[7][8][9]14 In some cases the temperature dependence crosses from metallic to semiconducting and weak localization behavior arises just above T c . Second, except near the critical concentration x cr where the insulator to metal transition occurs, 10 T c is almost independent of the doping level x whereas the Fermi level DOS undergoes a change as doping is increased.…”