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Magnetic quantum-critical phenomena

(For a PhD PROJECT on pressure-tuning of electronic matter with focus on magnetism and superconductivity click here)

 

Many metals show striking quantum-critical behaviour in a wide temperature range above magnetic quantum phase transitions. Strong deviations from normal metallic (Fermi liquid) behaviour as well as novel phases (including unconventional superconductivity) have been observed (figure).

niklowitz-genphasediag

Our strategy has been to study systems with relatively simple crystal and electronic structures and bring them into the quantum-critical regime using the highly controlled methods of high-pressure and magnetic-field tuning.

In the past we studied NiS2, which becomes an antiferromagnetic metal at high pressure.[1] At the antiferromagnetic quantum phase transition, NiS2 shows an intriguing temperature dependence in the resistivity exponent, which indicates short-circuiting of so-called “hot regions“ (susceptible to antiferromagnetic spin-fluctuations) of the Fermi surface by “cold regions”.

The weakly ferromagnetic metal Ni3Al reveals a dramatically extended region of a non-Fermi-liquid state in the pressure-temperature phase diagram, which resembles a Marginal Fermi liquid state,[2] an electronic state of great interest predicted in the context of high-temperature superconductivity and in other fields.

In experiments on antiferromagnetic stoichiometric YbAgGe we have revealed that strong non-Fermi liquid behaviour can be induced by the application of an external magnetic field.[3] Curious frustration effects in the quasi-elastic dispersion, seen in neutron scattering experiments at zero field, suggest that localisation and destruction of heavy quasiparticles might play an important role in this compound.[4]

We are testing further aspects for weakly magnetic metals, e.g. the predicted instability of continuous ferromagnetic quantum phase transitions against modulated order.

 

in collaboration with U Cambridge, TU Munich CEA Grenoble, Iowa State University, UCL

 

[1] PG Niklowitz, MJ Steiner, GG Lonzarich, D Braithwaite, G Knebel, J Flouquet, JA Wilson, ”Unconventional resistivity at the border of metallic antiferromagnetism in NiS2”, Phys.Rev.B 77 (2008) 115135.

[2] PG Niklowitz, F Beckers, GG Lonzarich, G Knebel, B Salce, J Thomasson, N Bernhoeft, D Braithwaite, J Flouquet, “Spin-fluctuation dominated electrical transport of Ni3Al at high pressure”, Phys.Rev.B 72 (2005) 24424.

[3] PG Niklowitz, G Knebel, J Flouquet, SL Bud’ko, PC Canfield, “Field-induced non-Fermi-liquid resistivity of stoichiometric YbAgGe single crystals”, Phys.Rev.B 73 (2006) 125101.

[4] B Fåk, DF McMorrow, PG Niklowitz, S Raymond, E Ressouche, J Flouquet, PC Canfield, SL Budko, Y Janssen, MJ Gutmann, “An inelastic neutron scattering study of single-crystal heavy-fermion YbAgGe”, J. Phys.: Condens. Matter 17 (2005) 301-311.

 


 

 

Quantum matter

 

 
 
 
 

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