and therefore showing no contrast in the spin-polarized measurements. A zero-energy peak in
measurements of P(E) in spin-polarized STM
(Fig. 3A) is caused by the nonlocal nature of the
MZM background and constitutes a unique signature of these excitations, allowing us to distinguish them from trivial edge modes.
Looking beyond our atomic-chain Majorana
platform, spin-selective spectroscopy measurements using quantum dots have been recently
proposed for the semiconducting nanowire
Majorana platform (33). As we have done in this
study for the atomic chains, such experiments are
expected to distinguish between trivial and nontrivial edge modes and probe the nonlocal nature
of MZMs in the nanowire platform. The spin polarization of MZMs may provide a useful approach to creating highly polarized spin currents
and entangling these topological localized quantum states with conventional spin qubits. In fact,
there are proposals outlining how a hybrid system
of spin and MZM qubits can be used to perform
universal quantum computation (34). The possibility that electron tunneling between spin qubits
(based on quantum dots or individual defects)
and MZMs can realize a quantum superposition
between the two is intriguing. Such a process
could, for example, facilitate long-distance entanglement between spatially well-separated spin
Note added in proof: After submission of our
manuscript, a spin-polarized STM study of Co
chains on Pb(110) was reported (36). The spin
polarization of the Shiba bands on such chains
also shows the antisymmetric features (with bias)
and is consistent with our results and analysis.
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We acknowledge discussions with L. Glazman, F. von Oppen,
K. Franke, P. Lee, and C. Kane. This work has been supported by the
Gordon and Betty Moore Foundation as part of the EPiQS initiative
(GBMF4530), the Office of Naval Research (grants ONR-N00014-14-1-
0330, ONR-N00014-11-1-0635, and ONR-N00014-13-1-0661), NSF
MRSEC (Materials Research Science and Engineering Centers)
programs through the Princeton Center for Complex Materials (award
DMR-1420541), NSF award DMR-1608848, a Simons Investigator
Award, NSF EAGER (Early-concept Grants for Exploratory Research)
award NOA-AWD-1004957, the Department of Energy’s Office of
Basic Energy Sciences, the Packard Foundation, Army Research
Office MURI (Multidisciplinary University Research Initiatives)
program W911NF-12-1-046, and the Eric and Wendy Schmidt
Transformative Technology Fund at Princeton. This project was also
made possible by the facilities at Princeton Nanoscale Microscopy
Laboratory. B.A.B. thanks Ecole Normale Superieure, UPMC
(Université Pierre et Marie Curie) Paris, and Donostia International
Physics Center for their generous sabbatical hosting. A. Y. ackno wledges
the hospitality of the Aspen Center for Physics, supported by NSF
award PHY-1607611. The data presented in this paper are available
from the corresponding author upon reasonable request.
Materials and Methods
Figs. S1 to S10
3 April 2017; accepted 29 September 2017
Published online 12 October 2017
How the news media activate public
expression and influence
Gary King,1 Benjamin Schneer,2 Ariel White3
We demonstrate that exposure to the news media causes Americans to take public stands
on specific issues, join national policy conversations, and express themselves publicly—all
key components of democratic politics—more often than they would otherwise. After
recruiting 48 mostly small media outlets, we chose groups of these outlets to write and
publish articles on subjects we approved, on dates we randomly assigned. We estimated the
causal effect on proximal measures, such as website pageviews and Twitter discussion of
the articles’ specific subjects, and distal ones, such as national Twitter conversation in broad
policy areas. Our intervention increased discussion in each broad policy area by ~62.7%
(relative to a day’s volume), accounting for 13,166 additional posts over the treatment
week, with similar effects across population subgroups.
The fields of political communication in gen- eral and media effects in particular are broad, deep, methodologically sophisticated, and central to social science. They have covered persuasion (1), agenda setting (2, 3), attitude
formation (4), diffusion, gatekeeping (5), priming
and agenda setting (6), issue framing (7), and numerous other topics, and are built on a wide range
of intellectual traditions [(8), p. 174].
We focus here on an aspect of political com-
munication with special relevance to the study of
representative democracy: how the news media
activate public expression, causing citizens to
discuss major issues of policy and politics as part
of the ongoing, collective “national conversa-
tion.” A well-functioning democracy larger than
the sum of individual attitudes and behaviors re-
quires public discussion and engagement among
citizens on major issues of the day (9–11). Indeed,
“political participation is not merely about trying
to influence policy but also about trying to induce
others to participate and give voice” (12). Although
governments may easily dismiss any individual’s
opinion, collective public expression has a power-
ful impact on the behavior of government officials
and the public policies they promulgate. The
power of collective expression is a central feature
of both representative democracy—where “the
more the people are aware of each other’s opin-
ions, the stronger the incentive for those who
776 10 NOVEMBER 2017 • VOL 358 ISSUE 6364 sciencemag.org SCIENCE
1Institute for Quantitative Social Science, Harvard University,
Cambridge, MA 02138, USA. 2Department of Political
Science, Florida State University, Tallahassee, FL 32306,
USA. 3Department of Political Science, Massachusetts
Institute of Technology, Cambridge, MA 02139, USA.
*Corresponding author. Email: firstname.lastname@example.org