Sky C. Cheung

Ferromagnetic ordering in superatomic solids.

In order to realize significant benefits from the assembly of solid-state materials from molecular cluster superatomic building blocks, several criteria must be met. Reproducible syntheses must reliably produce macroscopic amounts of pure material; the cluster-assembled solids must show properties that are more than simply averages of those of the constituent subunits; and rational changes to the chemical structures of the subunits must result in predictable changes in the collective properties of the solid. In this report we show that we can meet these requirements. Using a combination of magnetometry and muon spin relaxation measurements, we demonstrate that crystallographically defined superatomic solids assembled from molecular nickel telluride clusters and fullerenes undergo a ferromagnetic phase transition at low temperatures. Moreover, we show that when we modify the constituent superatoms, the cooperative magnetic properties change in predictable ways.

(Ca,Na)(Zn,Mn)2As2: A new spin and charge doping decoupled diluted ferromagnetic semiconductor

Here we report the successful synthesis of a spin-&charge-decoupled diluted magnetic semiconductor (Ca,Na)(Zn,Mn)2As2, crystallizing into the hexagonal CaAl2Si2 structure. The compound shows a ferromagnetic transition with a Curie temperature up to 33 K with 10% Na doping, which gives rise to carrier density of np~10^20 cm^-3. The new DMS is a soft magnetic material with HC<400 Oe. The anomalous Hall effect is observed below the ferromagnetic ordering temperature. With increasing Mn doping, ferromagnetic order is accompanied by an interaction between the local spin and mobile charge, giving rise to a minimum in resistivity at low temperatures and localizing the conduction electrons. The system provides an ideal platform for studying the interaction of the local spins and conduction electrons.Here, we report the successful synthesis of a spin- and charge-decoupled diluted magnetic semiconductor (DMS) (Ca,Na)(Zn,Mn)2As2, crystallizing into the hexagonal CaAl2Si2 structure. The compound shows a ferromagnetic transition with a Curie temperature up to 33 K with 10% Na doping, which gives rise to carrier density of np ∼ 1020 cm−3. The new DMS is a soft magnetic material with HC < 400 Oe. The anomalous Hall effect is observed below the ferromagnetic ordering temperature. With increasing Mn doping, ferromagnetic order is accompanied by an interaction between the local spin and mobile charge, giving rise to a minimum in resistivity at low temperatures and localizing the conduction electrons. The system provides an ideal platform for studying the interaction of the local spins and conduction electrons.

(Sr, Na)( Zn, Mn)(2)As-2: A diluted ferromagnetic semiconductor with the hexagonal CaAl2Si2 type structure

A new diluted ferromagnetic semiconductor (Sr, Na)(Zn, Mn) As-2(2) is reported, in which charge and spin doping are decoupled via Sr/Na and Zn/Mn substitutions, respectively, being distinguished from classic (Ga, Mn) As, where charge and spin doping are simultaneously integrated. Different from the recently reported ferromagnetic (Ba, K)(Zn, Mn) 2As2, this material crystallizes into the hexagonal CaAl2Si2 type structure. Ferromagnetism with a Curie temperature up to 20 K has been observed from magnetization. The muon spin relaxation measurements suggest that the exchange interaction between Mn moments of this new system could be different from the earlier diluted magnetic semiconductors (DMS) systems. This system provides an important means for studying ferromagnetism in DMS.

Signatures of the topological s +− superconducting order parameter in the type-II Weyl semimetal T d -MoTe 2

Possible topologically non-trivial superconducting order parameter in type-II Weyl semimetal Td-MoTe2 Z. Guguchia, ∗ F.v. Rohr, Z. Shermadini, A.T. Lee, S. Banerjee, A.R. Wieteska, C.A. Marianetti, H. Luetkens, Z. Gong, B.A. Frandsen, S.C. Cheung, C. Baines, A. Shengelaya, 7 A.N. Pasupathy, E. Morenzoni, S.J.L. Billinge, 8 A. Amato, R.J. Cava, R. Khasanov, and Y.J. Uemura Department of Physics, Columbia University, New York, NY 10027, USA Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA Department of Physics, University of California, Berkeley, California 94720, USA Department of Physics, Tbilisi State University, Chavchavadze 3, GE-0128 Tbilisi, Georgia Andronikashvili Institute of Physics of I.Javakhishvili Tbilisi State University, Tamarashvili str. 6, 0177 Tbilisi, Georgia Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USAIn its orthorhombic Td polymorph, MoTe2 is a type-II Weyl semimetal, where the Weyl fermions emerge at the boundary between electron and hole pockets. Non-saturating magnetoresistance and superconductivity were also observed in Td-MoTe2. Understanding the superconductivity in Td-MoTe2, which was proposed to be topologically non-trivial, is of eminent interest. Here, we report high-pressure muon-spin rotation experiments probing the temperature-dependent magnetic penetration depth in Td-MoTe2. A substantial increase of the superfluid density and a linear scaling with the superconducting critical temperature Tc is observed under pressure. Moreover, the superconducting order parameter in Td-MoTe2 is determined to have 2-gap s-wave symmetry. We also exclude time-reversal symmetry breaking in the superconducting state with zero-field μSR experiments. Considering the strong suppression of Tc in MoTe2 by disorder, we suggest that topologically non-trivial s+− state is more likely to be realized in MoTe2 than the topologically trivial s++ state.Understanding the superconductivity in topological materials is of eminent interest. Here, Guguchia et al. report temperature-dependent magnetic penetration depth in the superconducting state of Td-MoTe2 under pressure, suggesting a topologically nontrivial s+− order parameter.

Uniaxial pressure effect on the magnetic ordered moment and transition temperatures in BaFe2-xTxAs2 ( T=Co,Ni )

We use neutron diffraction and muon spin relaxation to study the effect of in-plane uniaxial pressure on the antiferromagnetic (AF) orthorhombic phase in BaFe

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning

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The synthesis and characterization of 1 1 1 1 type diluted ferromagnetic semiconductor (La(1-x)Ca(x))(Zn(1-x) Mn(x))AsO.

As

New Fluoride-arsenide Diluted Magnetic Semiconductor (Ba,K)F(Zn,Mn)As with Independent Spin and Charge Doping

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Antiferromagnetism and hidden order in isoelectronic doping of URu2Si2

and its Co- and Ni-substituted members near optimal superconductivity. In the low temperature AF ordered state, uniaxial pressure necessary to detwin the orthorhombic crystals also increases the magnetic ordered moment, reaching an 11

Author Correction: Signatures of the topological s+− superconducting order parameter in the type-II Weyl semimetal Td-MoTe2

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