1. B4 Single crystal growth of tunable quantum spin systems
Franz Ritter, Cornelius Krellner (Goethe-Universität Frankfurt)
Achievements
2D triangular lattices
Project goals and work program
2D kagome lattices
Cs2CuCl4
Pnma
Growth at 24°C
Pnma
Growth at 24°C
Cs2CuBr4
AF coupled Cu2+-spins
Various 2D geometries
Pronounced frustration
ZnCu3(OH)6Cl2
Cs2CuCl3Br
Growth at 50°C
Cs2CuCl2Br2
Growth at 50°C A3 A5
A10 B1 B2 B3
Paramagnetic
Spin Liquid
3D AFM
polarized FM
Field (T) 5 4 3 2 1
Temperature (K)
Dominant coupling J ~ 4.4 K along b (“chains”)
Zigzag coupling J’ along c (“interchain”)
Increasing frustration, J’/J ® 1 with x in Cs2Cu(Cl4-xBrx)
2D kagome planes stacked along c
Dominant coupling: J1~ 180 K (nn kagome)
J3/J1 ~ 0.02 (2nd nn kagome)
Interlayer coupling: J2/J1 ~ 0.03
H. Jeschke et al., Phys. Rev. B 88, (2013)
Model system: MCu3(OH)6X2 A3 A5 A8
A10 B1 B2 B3
B7E
B13N
Achievements
Large Pnma-type single crystals for all x
S. Streib et al., Phys. Rev. B 91, (R) (2015)
M.A. Fayzullin et al., Phys. Rev. B 88, (2013)
Site-selective occupation of Br atoms on halogen sites for x = 1 and 2
Pronounced anisotropic thermal expansion
Strong variation of the local Cu environment as function of T and x
N. van Well et al., Phys. Rev. B 91, (2015)
x = 0
x = 1
x = 2
x = 4
Setup of a hydrothermal reactor with T = 250°C and up to 200 bar
Hydrothermal crystal growth of Herbertsmithite ZnCu3(OH)6Cl2
Synthesis of barlowite, Cu4(OH)6BrF
T.-H. Han et al., PRL 113, (2014)
with new synthetic approach:
CuBr2 + CuO + NH4F  Cu4(OH)6BrF A8
Barlowite
Cu4(OH)6BrF B1
Theoretical proposed correlated Dirac metal
in an electron-doped kagome lattice:
Nature Commun. 5, 4261 (2014)
Ga-substituted herbertsmithite, GaxCu4-x(OH)6Cl2 B2
GaxCu4-x(OH)6Cl2
x = 0.6(2)
50 µm
Pronounced T-dependence of the calculated magnetic exchange couplings, from the experimental structure data for Cs2CuCl4
Calculated low-T data match the established J-values from neutron scattering experiments
N. van Well et al., Phys. Rev. B 91, (2015)
Project goals and work program B2
Magnetic contribution to the specific-heat for Cs2Cu(Cl4-xBrx)
Successful crystal growth of non- magnetic reference Cs2Zn(Cl4-xBrx)
Single crystal growth of barlowite, Cu4(OH)6BrF
Towards an ideal kagome lattice through non-magnetic substitution on the interlayer position in barlowite-typed systems:
 MCu3(OH)6BrF with M = Zn, Sn, Mg, …
 MCu3(OH)6ClF with M = Zn, Sn, Mg, …
Towards an electron-doped kagome lattice through trivalent substitution on the interlayer position in herbertsmithite-typed systems:
 MCu3(OH)6Cl2 with M = Ga, Sc, Y, Al, …
Optimization of the crystal growth conditions for the most promising substitution series
Structural and chemical characterization of the novel materials
Determination of the magnetic ground state using susceptibility and specific heat measurements
Cs2 ZnBr4 B2
Structural phase stability at low temperatures
Continuing the single crystal growth of x = 0, 1, 2, 4
Determination of the magnetic ground state for x = 1 and 2
Determination of coupling constants for 0 < x < 4 B1 B1
B13N
Transregional Collaborative Research Centre SFB/TR 49
Frankfurt / Kaiserslautern / Mainz