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Quantum spin liquid in organo-metallic magnet
Collin Broholm, Johns Hopkins University, DMR 0074571
There are many types of magnets including
ferromangets, antiferromagnets, ferrimagnets,
even spin-glasses. Apart from revealing the rich
phenomena that emerge when many dipoles
interact, such materials are also cornerstones
for modern technologies.
We have encountered a new type of magnetic
phase in the organo-metallic material, PHCC
(C4H12N2Cu2Cl6). Despite interactions that define
a two-dimensional spin lattice (Fig. 1), quantum
fluctuations are so strong that there is no static
order even as temperature approaches zero.
The situation is analogues to liquid helium,
where quantum fluctuations prevent freezing.
While quantum disordered phases are common
in one-dimensional magnets, PHCC is a unique
two dimensional case. Our experiments show
that competing frustrated interactions enhance
fluctuations and help to suppress long range
order. Conventional magnetism can be “turned
on” by a magnetic field or by non-magnetic
impurities like the electronic conduction in a
semiconductor and therein may lie future
applications of these systems.
Fig. 1. Structure
of PHCC with
spin-1/2 Cu in
red, and satisfied
and
frustrated
bonds in blue and
green
respectively.
Fig. 2. Phase diagram of PHCC with a quantum
disordered (QD), long range-ordered (LRO), thermally
disordered (TD), and ferromagnetic (FP) phase.
Educating a new generation of neutron physicists
Collin Broholm, Johns Hopkins University, DMR 0074571
Neutron scattering is a unique tool for
probing structure and dynamics in
condensed matter on the nano-scale length
scale and pico-second time scale. While the
technique was invented on the American
Continent in the fifties, few neutron
scientists were educated in the US since.
The US is now building the worlds best
spallation neutron source at a cost of $1.4B.
Situated close to the NIST Center for
Neutron Research, our NSF funded project
is in a unique position to educate innovative
scientists that can harvest the full potential
of US neutron sources. Four graduates of
our program are now, employed at National
Facilities for neutron scattering. Three Ph.
D. students will graduate this spring of
which one goes to an academic post
doctoral position and two take up neutron
scattering post doctoral positions at NIST
and LANL. Dr. Broholm is also promoting
this important technique through lectures at
many levels.
Fig. 3. The SPINS cold neutron spectrometer at the NIST
for neutron research. Dr. Broholm helped to build this
instrument and experiments for three Ph. D. thesis funded
by DMR 0074571 were performed there. The tall cylindrical
object is an 11.5 T dilution fridge funded in part by NSF
through Johns Hopkins University.