Sokol Research Group: Indiana University Bloomington

Sample cell used in millikelvin neutron scattering studies attached to the cold stage of a dilution refrigerator

Phonon-maxon-roton spectrum of helium in 2 nm pores (*Prisk et.al. PRB 88, 14521* )

Behavior of micelles studied with SANS (*Das et. al. Langmuir 28, 11962*)

Research

Our work focuses on the study of the structure and dyanmics of condensed matter systems under confinement at the nanoscale. Confinement in nanometer size pores or on surfaces can drastically affect the properties of confined systems ranging from classical solids to quantum liquids and can even lead to new phases not present in the bulk. We use neutron and x-ray scattering to probe the microscopic structure and dynamics of these confined systems.

Featured Articles

**Bulklike excitations in nanoconfined liquid helium, Bryan, M. S., Prisk, T. R. Sherline, T. E., Diallo, S. O., & Sokol, P. E. Physical Review B, 95(14), 144509.** High resolution inelastic neutron scattering studies of the the roton in nanoscale confined helium show that the lifetime is the same as in the bulk liquid. At low temperatures this corresponds to a mean free path thousands of times longer than the pore size implying that the lifetime is not set by the scale of the confinement.

**Diffusive and rotational dynamics of condensed n-H₂ confined in MCM-41. Prisk, T. R., Bryan, M. S., & Sokol, P. E. (2014). *Physical Chemistry Chemical Physics : PCCP*, 16(33), 17960–74.** Inelastic neutron scattering is used to study the diffusive and rotational dynamics of hydrogen molecules confined in 3.5 nm pores of MCM-41. The studies provide information of the orientational potential at the surface which leads to selective adsorption of ortho-H2.

The new cold neutron chopper spectrometer at the Spallation Neutron Source: Design and performance. Ehlers, G., Podlesnyak, a. a., Niedziela, J. L., Iverson, E. B., & Sokol, P. E. (2011). *Review of Scientific Instruments*, 82(8), 85108. The Cold Neutron Chopper Spectrometer (CNCS) is a world class inelastic spectrometer at the Spallation Neutron Source. The design and construction of the instrument was a join effort between the Sokol Group and Oak Ridge National Lab.

Group News

June 21, 2018 - Moving into the new lab

Moving equipment into the new lab in the renovated Swain Hall. Looks like most of the utilities are ready - unlike our temporary relocation to MES Hall.

June 19, 2018 - Moving Day

Two rotating anode x-ray generators are loaded onto a flat bed trailer for the move back to Swain Lab. Fortunately the rain predicted for the day held off until the move was complete.

June 15, 2018 - Getting ready for move to renovated Lab

After 2 years in temporary lab space at the Multidisciplinary Engineering and Science Hall the lab is getting prepared to move back to newly renovated laboratory space in Swain Hall.

May 22, 2018 - Paper avaialble at PRB On-line

"Maxon and roton measurements in nanoconfined ⁴He" by Matt Bryan and Paul Sokol has appeared on-line in Physical Review B

May 14, 2018 - New paper in arXiv

A manuscript describing the filling dependence of the maxon and roton in ⁴He has been posted on arXiv. Previous studies have suggested that the confined liquid behaves as a bulk liquid at negative pressures and that the maxon provided a direct measure of the pressure. This study shows that the maxon and roton imply different desnities of the confined liquid and that it cannot be treated simply as a bulk liquid at negative pressures.

Feb 28, 2018 - Sokol and Del Maestro receive NSF Funding

Adrian Del Maestro (University of Vermont) and Paul Sokol receive funding from the Condensed Matter Physics and the Condensed Matter and Matterials Theory programs in the Division of Materials Research at NSF for a joint experimental and theoretical effort to study the Luttinger Liquid behavior of ⁴He confined in 1 dimensional channels.

July 24, 2017 - New Paper published in JLTP

"The Momentum Distribution of Liquid 4He" appears in the Journal of Low Temperature Physics. This joint experimental and theoretical study observes excellent agreement between experimental measurements of the momentum distribution and Quantum Mante Carlo of the momentum distribution and final state effects as a function of temoerature.

April 20, 2017 - New paper published in Physical Review B

"Bulklike excitations in nanoconfined helium" appears in Physical Review B. This study shows that the roton lifetime in confinement is identical in the bulk indicating rotons scatter elastically at the pore walls.