1.3 Superconducting Materials

Magnetic interactions are likely to play a key role in mediating superconductivity in the recently discovered family of iron pnictides; however, their character is not yet well understood. In particular, whether the system is best de- scribed in terms of large, local magnetic moments centered at each Fe site, in which case elementary excitations are collective spin waves (SWs) or are itinerant (elementary excitations characterized by single-particle electron-hole transitions) is a subject of great debate.

Low-energy coherent Stoner-like excitations in CaFe $_{2}$ As $_{2}$
Liqin Ke, M. van Schilfgaarde, J. Pulikkotil, T. Kotani, and V. Antropov.
Phys. Rev. B: Rapid communication, 83:060404, (2011) Editors’ Suggestion

$(a) $N(E)$ is shown in units of eV$^{-1}$ per cell containing one Fe atom in CaFe$_2$As$_2$. Data are shown for $M = 0.4$ μB and 1.1 μB. Both kinds of transitions are reflected in peaks in $\chi_0 (q = 0, \omega)$, shown in panel (c) for $M$=0.4 μB , 0.8 μB , and 1.1 μB . (b) $N(E_\text{F})$ is shown as a function of moment $M$. The blue vertical bar denotes the experimental moment. It also approximately demarcates the transition from itinerant to localized behavior. (c) The bare susceptibility $\chi_0(q = 0,\omega)$ is in the same units. The text discusses the significance of the arrows in panels (a) and (c).$

Figure 1.3: (a) $N(E)$ is shown in units of eV $^{-1}$ per cell containing one Fe atom in CaFe $_2$ As $_2$ . Data are shown for $M = 0.4$ μB and 1.1 μB. Both kinds of transitions are reflected in peaks in $\chi_0 (q = 0, \omega)$ , shown in panel (c) for $M$ =0.4 μB , 0.8 μB , and 1.1 μB . (b) $N(E_\text{F})$ is shown as a function of moment $M$ . The blue vertical bar denotes the experimental moment. It also approximately demarcates the transition from itinerant to localized behavior. (c) The bare susceptibility $\chi_0(q = 0,\omega)$ is in the same units. The text discusses the significance of the arrows in panels (a) and (c).

2022 (Krenkel et al. 2022)
2021 (Ueland et al. 2021; Pakhira et al. 2021; Islam et al. 2020)
2020 (Timmons et al. 2020)
2019 $\ge$ (Wysocki et al. 2013; Ke and Schilfgaarde 2012; Ke, Schilfgaarde, and Antropov 2012; Ke et al. 2011; Pulikkotil et al. 2010)

Publications

Islam, Farhan, Elijah Gordon, Pinaki Das, Yong Liu, Liqin Ke, Douglas L. Abernathy, Robert J. McQueeney, and David Vaknin. 2020. “Spin Dynamics in Antiferromagnetic Oxypnictides and Fluoropnictides: LaMnAsO, LaMnSbO, and BaMnAsF.” Phys. Rev. B 101: 155119. https://doi.org/10.1103/PhysRevB.101.155119.

Ke, Liqin, Mark van Schilfgaarde, and Vladimir Antropov. 2012. “Doping-Induced Metallicity and Coexistence of Magnetic Subsystems in K

$_2$ Fe

$_{4+x}$ Se

$_5$ .” Solid State Communications 152 (19): 1846–49. https://doi.org/https://doi.org/10.1016/j.ssc.2012.06.011.

Ke, Liqin, Mark van Schilfgaarde, Jiji Pulikkotil, Takao Kotani, and Vladimir Antropov. 2011. “Low-Energy Coherent Stoner-Like Excitations in CaFe

$_{2}$ As

$_{2}$ .” Phys. Rev. B: Rapid Communication 83: 060404. https://doi.org/10.1103/PhysRevB.83.060404.

Ke, Liqin, and Vladimir van Schilfgaarde Mark aand Antropov. 2012. “Spin Excitations in K

$_2$ Fe

$_{4+x}$ Se

$_5$ : Linear Response Approach.” Phys. Rev. B: Rapid Communication 86: 020402. https://doi.org/10.1103/PhysRevB.86.020402.

Krenkel, E. H., M. A. Tanatar, M. Kończykowski, R. Grasset, E. I. Timmons, S. Ghimire, K. R. Joshi, et al. 2022. “Possible unconventional pairing in (Ca,Sr)

$_3$ (Ir,Rh)

$_{4}$ Sn

$_{13}$ superconductors revealed by controlling disorder.” Phys. Rev. B 105: 094521. https://doi.org/10.1103/PhysRevB.105.094521.

Pakhira, Santanu, Y. Lee, Liqin Ke, V. Smetana, A.-V. Mudring, Thomas Heitmann, David Vaknin, and D. C. Johnston. 2021. “Suppression of Antiferromagnetic Order and Strong Ferromagnetic Spin Fluctuations in Ca(Co

$_{1-x}$ Ni

$_x$ )

$_{2-y}$ As

$_2$ Single Crystals.” Phys. Rev. B 104: 094420. https://doi.org/10.1103/PhysRevB.104.094420.

Pulikkotil, Jiji, Liqin Ke, Mark van Schilfgaarde, Takao Kotani, and Vladimir Antropov. 2010. “Magnetism and Exchange Coupling in Iron Pnictides.” Superconductor Science and Technology 23 (5): 054012. http://stacks.iop.org/0953-2048/23/i=5/a=054012.

Timmons, E. I., S. Teknowijoyo, M. Ko ńczykowski, O. Cavani, M. A. Tanatar, Sunil Ghimire, Kyuil Cho, et al. 2020. “Electron irradiation effects on superconductivity in

${\mathrm{PdTe}}_{2}$ : An application of a generalized Anderson theorem.” Phys. Rev. Research 2 (May): 023140. https://doi.org/10.1103/PhysRevResearch.2.023140.

Ueland, B. G., Santanu Pakhira, Bing Li, A. Sapkota, N. S. Sangeetha, T. G. Perring, Y. Lee, Liqin Ke, D. C. Johnston, and R. J. McQueeney. 2021. “Carrier tuning of Stoner ferromagnetism in ThCr

$_2$ Si

$_2$ -structure cobalt arsenides.” Phys. Rev. B 104: L220410. https://doi.org/10.1103/PhysRevB.104.L220410.

Wysocki, A L, K D Belashchenko, L Ke, M van Schilfgaarde, and V P Antropov. 2013. “Biquadratic Magnetic Interaction in Parent Ferropnictides.” Journal of Physics: Conference Series 449 (1): 012024. http://stacks.iop.org/1742-6596/449/i=1/a=012024.