Dr. Qianhui Mao [Department of Physics, Zhejiang University]

Title: Superconductivity, magnetism and magnetocaloric effect in Tl-based 3d metallic chalcogenides

Time: 2:00 - 3:00 PM, Friday, April 29, 2016

Place: Conference Room 201, Building 6, HPSTAR (Shanghai)

Host: Dr. Xiaojia Chen

Abstract:

Interplay between superconductivity (SC) and magnetism is one of the central topics in condensed matter physics. Up to now, unconventional SC has been discovered in many 3d-element based materials and only Ni-based SC seems to be an exception. We challenge this conclusion by investigating the phase diagram of     Tl (Co1-xNix)2Se2 and Tl (Co1-xNix)2S2 1. It is found that TlNi2(Se, S)2 2, 3 are multiband nodeless superconductors and SC in these two systems has close relationship with A-type antiferromagnetism, implying its unconventional nature. However, Ni serves as nonmagnetic dopant and magnetism in these systems is heavily diluted. Thus, it is crucial to investigate TlCo2Se2 and TlCo2S2 under pressure. To elucidate the intrinsic magnetic interaction, we have studied the critical property of ferromagnetic TlCo2S2 and a tricritical behavior is uncovered 4. We also identified a large low field magnetocaloric effect (MCE) in a quasi-one dimensional compound TlFe3Te3. Besides large MCE, the low-level thermal and field hysteresis makes this material outstanding among the magnetic refrigerants 5. Since the crystal structure of TlFe3Te3 is similar to that of unconventional superconductor K2Cr3As3, weather Curie temperature could be suppressed by pressure in TlFe3Te3 to give unconventional superconductivity is also under our consideration.

References:

1.Q. H. Mao et al., (in preparation).

2.H. D. Wang, Q. H. Mao et al., Phys. Rev. Letts. 111, 207001 (2013). [Editors’ Suggestions].

3.H. D. Wang, Q. H. Mao et al., J. Phys.: Condens. Matter. 27, 395701 (2012).

4.Q. H. Mao et al., “From tricritical ferromagnetism to metamagnetism in Tl (Co1-xNix)2S2   (x = 0, 0.05)” (in submission).

5.Q. H. Mao et al., “Large low field magnetocaloric effect in first-order phase transition compound TlFe3Te3 with low-level hysteresis” (in submission).

Biography of the Speaker:

Qianhui Mao completed his bachelor’s degree in Applied Physics at Henan Polytechnic University. After that, he moved to Zhejiang University for his Ph.D. study under the supervision by Prof. Minghu Fang. His researches focus on unconventional superconductivity and its interplay with magnetism in strongly correlated systems. His work on Tl(Co1-xNix)2Se2 and Tl(Co1-xNix)2S2 renews their phase diagrams and may expand the exploration on unconventional superconductivity.