Presentation Information
[PCP1-13]Observation of Tc dependence of gapped quasiparticle density of states in layered nitride chloride superconductor a-AxTiNCl by STM/STS
*Akira Sugimoto1, Masashi Tanaka2, Toshikazu Ekino1, Alexander M Gabovich3 (1. Graduate School of Advanced Science and Engineering, Hiroshima University (Japan), 2. Kyusyu Inst. of Tech. (Japan), 3. Institute of Physics of the National Academy of Sciences, Ukraine (Ukraine))
Keywords:
Layered nitride chloride superconductor,STM/STS,superconducting gap,pseudogap
The layered nitride chloride alpha-AxTiNCl (A=alkali metal) exhibits superconductivity of up to Tc=18 K when the layered pristine alpha-TiNCl semiconductor is intercalated by alkali metal atoms. In this superconductor, an anomalously large energy gap Eg was frequently observed1-3 with the ratio 2Eg/kBTc = 8 – 16, where kB is Boltzmann constant. Such a ratio is far above the values in conventional superconductors and is often observed when the competing order appears. We have carried out STM/STS measurements of layered superconducting Na0.25TiNCl with different Tc, and investigated the relationship between Tc and the energy gap size revealed in dI/dV curves (See Fig. 2). Fig. 1 shows a histogram of |Eg| obtained from the entire STS-probed region. The gap-peak positions observed on the negative bias side of the dI/dV curve was identified with the energy Eg values (see inset of Fig. 1). Fig. 2 compares the average values |Eg|(ave) with Tc. One sees that the gap |Eg| increases as Tc decreases. This behaviour is the opposite to that of BCS-like superconductors of whatever order-parameter symmetry. However, it is rather similar to what is observed in underdoped cuprate superconductors, where the so-called pseudogap manifests itself along with the true superconducting gap. The spread of the Tc in our NaxTiNCl samples is probably due to the spatial disorder in the charge carrier distribution caused by the annealing temperature regime during Na intercalation4. This is like the situation in cuprates, where pseudogap values decrease with oxygen doping.
References
1) A. Sugimoto et al, Phys.Rev. B 85,144517 (2012).
2) K. Matsumoto et al, JPS Conf. Proc. 38, 011035 (2023).
3) A. Sugimoto et al, Low Temp. Phys. 49, 870 (2023).
4) M. Tanaka & N. Kataoka et al, Mater. Res. Bull. 153, 111896 (2022).
References
1) A. Sugimoto et al, Phys.Rev. B 85,144517 (2012).
2) K. Matsumoto et al, JPS Conf. Proc. 38, 011035 (2023).
3) A. Sugimoto et al, Low Temp. Phys. 49, 870 (2023).
4) M. Tanaka & N. Kataoka et al, Mater. Res. Bull. 153, 111896 (2022).